rnia 
1 


BRIGK^CLAYRECORD 

O  t-i  I  O  -^>,C3  O 


UNIVERSITY  OF  CALIFORNIA 
LOS  ANGELES 


GIFT  OF 

James  W.  Lfoncrieff 


CLAYWORKING    PROBLEMS 


CLAYWORKING    PROBLEMS 

Being  One  Hundred  and  One 
"Questions  and  Answers" 
Selected  from  the  pages  of 

Brick    and    Clay    Record 

A  publication  devoted  to  the  many  branches 

of  the  clayworking  industry  and 

issued  semi-monthly. 


Chicago 
Brick  and  Clay  Record 

1915 
(All    Rights   Reserved) 


Copyright,    1915, 

by 

I '.rick  and  Clay  Record 
Chicago 


PREFACE 

IX  TWO  YEARS,  more  than  five  hundred  questions  inti- 
mately connected  with  clayworking,  have  been  mailed  to 
the  editorial  offices  of  "Brick  and  Clay  Record."  Possi- 
bly two-thirds  of  these,  having  presented  problems  that  bore 
evidences  of  being  of  value  to  more  than  one  plant,  were  an- 
swered through  the  columns  of  the  magazine. 

The  wide  range  of  these  questions  is  indicated  by  the  index 
which  is  a  part  of  this  volume.  The  quality  of  the  answers 
will  be  determined  by  the  reading. 

In  this  connection  it  is  well  to  quote  from  one  of  those  an- 
swers, using  the  language  of  R.  T.  Stull,  E.  M.  (in  Cer.) 
then  of  Urbana,  Illinois,  who  says: 

"No  doubt  you  have  read  Robert  Burns'  ode  to  a  famous 
physician  who  could  prescribe  curatives  based  upon  evidence 
sent  him  in  a  'Kale'  leaf.  There  are  no  doctors  in  this  day 
and  age  of  enlightenment,  who  are  as  wise  as  the  famous 
doctor  of  Burns'.  With  the  exception  of  a  few  simple  cases, 
the  'ceramic  doctor'  cannot  prescribe  intelligently  from  a  few 
symptoms  sent  him  by  mail." 

The  claim  is  made  by  some  who  possess  a  certain  knowl- 
edge, that  the  art  of  claycrafting  has  advanced  more  in  the 
last  ten  years  than  in  the  preceding  ten  thousand  years.  Per- 
haps it  would  have  been  simpler  to  have  said  that  it  has  ad- 
vanced more  in  the  last  ten  years  than  in  the  thirty  years 
preceding,  and  this  brings  the  period  within  the  memory  of 
some  of  our  compatriots.  At  any  rate,  there  has  been  a  great 
and  notable  improvement  in  methods,  machines  and  prod- 
ucts. 

The  changes  have  l>een  so  radical  that  much  of  the  wisdom 


PREFACE 


of  the  past  generation  has  become  as  superstition,  and  men 
who  were  experienced  in  many  brandies  of  clayworking,  and 
who  were  regarded  as  experts  but  a  few  years  ago,  now  find 
that  their  knowledge  is  as  worthless  as  the  ability  to  weave 
with  a  hand  loom  or  to  drive  four  oxen. 

The  position  of  a  trade  or  technical  publication  gives  it 
unexampled  facilities  for  the  gathering  of  the  best  informa- 
tion that  is  at  hand  in  the  industry  it  serves.  Its  news  col- 
umns tell  of  the  improved  products  and  methods,  while  its 
advertising  columns  speak  of  improved  machinery  and  appli- 
ances. The  system  of  inquiry  that  makes  it  possible  to  fill 
these  columns  with  something,  new  in  every  issue,  brings,  at 
the  same  time,  accurate  information  as  to  the  men  who  are 
responsible  for  the  advances  that  are  being  made. 

How  simple  it  is,  therefore,  for  a  trade  or  technical  publi- 
cation to  turn  to  the  best  source  of  knowledge  on  any  par- 
ticular point.  No  individual,  no  business  house — other  than 
a  publisher— could  do  this;  so  it  is  that  "Brick  and  Clay  Rec- 
ord," while  occupying,  to  some  extent,  the  position  of  Burns' 
doctor  (who  prescribed  by  mail)  has  given  solutions  to  in- 
tricate problems  which  have  come  to  it  in  precisely  the  same 
manner  as  did  the  Scotch  doctor — minus,  however,  the 
"kale." 

That  these  answers  have  been  right— that  they  have  solved 
problems — is  beyond  doubt,  for  the  men  who  asked  the  ques- 
tions have,  iu  many  cases,  later  written  to  say  that  they  have 
tried  the  solutions  offered  and  so  effected  actual  savings  in 
money,  in  time  and  in  product. 

The  immense  value  of  this  Department  of  Questions  and 
Answers  is  beginning  to  be  appreciated.  This  is  evidenced 
by  the  ever-increasing  number  of  inquiries  that  come  to  us. 

Without  these  inquiries,  the  Department  could  not  exist. 
Chicago,  1915. 


CONTENTS 


A 
*  Absorption   Tests  on   Pace-Brick  ...............  _  ......  _  ......  _  .....  134 

Alkaline  Clay  .................  _„  .............................  ________________  "    148 

Amortization  of  Bank  Indebtedness  ___________________  94 

Artificial  Drying:.  Effect  on  Clay  of-  ...........................  ____  ...................  166 

B 
Bank  Indebtedness,  Amortization  of  ...........................  _  .......  94 

Belting.  Care  of  ---------------------------  .......  ------------  .......................  116 

Black   Coring-  .......  ___________  ..........  _________  ......  ___  14 

Black  Enamel  for  Enamel  Brick  ...................  ________________  "".  65 

Blast  Furnace  Slag,  Brick  Made  from  ___________________________  ......  _101 

Blisters  on   Drain   Tile  _____  „        _          _    _  162 

Bloated  or  Swollen   Brick  .......  _____________________  ........  _"  _______  "'"".'"."'.  14 

Blue   Enamel   for  Enamel    Brick  ......  „  ......  ____  .....  ______________  ...............  65 

Glaze   for   Stoneware  -----------------------------------------------------  70 

V  Brick.   Absorption   Tests  on    Face-  Brick  --------------------------------  134 

Analysis   in   Sand-lime  ..............  ......  153 

Break   in    Drying  ________  ............................  _____________  ........  _  ................  167 

Color  Affected  by  Change  In  Fuel...-  ...........................  __  ......  ____  43 

Crack   In   Burning..—  ......  _________  ..........  ____  .....  ___________________  37 

Crack  in  Drying  ...........  _____________  ...........  _  ..................  ____________________  161 

Dipping  to   Change   Color  ................  ______  ......................  _______________  136 

Economy  of   Reburning  Soft  ................  _  .....................  ----------  ......  126 

Flashed  Heads  on  Gray  ___________________________  ..........  __________  .....  _____  121 

Made  from   Blast  Furnace  Slag  ______  ............  ___________________  101 

Making    Bullnoses    by    Hand  ___________________________________  ......  146 

Manuf  acture    of    Silica,  155 

Mash  in  Center  of  Kiln.~.'_.."."L!.L..™"!.L~  _____  !!.~"..^""_.!ZZ_.!1!  11 

Silica,  Manufacture  of  ..........  _  ........  ----------  .....  ______________  ..........  ___  155 

To  Produce  Red  Color  from  Buff  Burning  Clay  —  ..........  _____  117 

Brick  Press  Checks  Brick  .......................  _____  ..........  __________________  112-114 

Brickwork,  Mortar  Joints  for  Interior  __________  .........  ______  ...............  ___  98 

To   Remove   Efflorescence   from  ...............  _.  ...........  —  ......................  124 

Burning   ......................  ....«.....—  ..................................................  _  ...................  11 

Of  Alkaline"  ciay-_l  ----  LlZ""ZZZZ"ZIZ!ZZZ!""Z"!Z"l48 

Bullnoses,   Making   by  Hand  ......  ...........  146 

Calcining    Fire-clay..™  .........  .181 

Capacity  of  Dry   Pans  .......  _  ..............  „  ...............................  __  ....................  170 

Cement  Joints   in   Sewer   Pipe  _________  ..........  ______  ........  -----  .................  127 

Changed   Fuel  Affects  Color  of  Dry   Press  Brick.....  .....  _  ............  43 

Checks  Caused  by  Brick  Press  ..............................  __________________  ...........  112 

Chimney  Draft,  Substituting  for  Fan  .....  ..  .....................  ____  ......  108-109 

Alkaline  ________________  .........  _____________________________________  ......  148 


91 

Mixing   Shale   with 

149 

Indicating  of  Plastic  
The  Effect  of  Artificial  Drying  on  

158 
IIZIZI"™166 
140 

Slips  .          .   .                                         

.  ...165 

foal.  Comparative  Cost  of  Oil  and  

.    ...        155 

Dust  in  Brick  Burning  , 

„.„  33 

Economy  of  Various  Grades                  

...    147 

Separating  from  Fire  Clay  ~  ~  

_  93 

CONTENTS 


Coloring   Molding   Sand 128-149 

Mortar    101 

Color  of  Brick  Changed   by  Dipping 136 

Cones  vs.    Pyrometers 1-9 

Copyrighting  Trade  Names 97 

Cost   of  Car   Shipments   of   Clay 87 

Of  Clay  Haulage 91 

Of  Electric  Power 89-90 

Of  Natural  Gas  Fuel 88 

Cracked  Brick 37 

Cracks  in  Drain  Tile 51 

in   Stove   Linings 42 

Culvert    Pipe,    Burned    Clay    vs.    Galvanized 

D 

Dies   79 

Die  Lamination 79 

Difficulty  in  Grinding  Wet  Shale 178 

Dipping  Brick  to  Change  Color 136 

Discoloration  in  Painted  Hollow  Tile  Walls 178 

"Doby"   Clay  Burns  Many   Colors 35 

Down-Draft  Kilns,   Changing  Up-Draft  to 54 

Proper    Size    of 49 

Draft,    Substituting   Chimney   for   Fan 108 

Drain  Tile,   Blisters  on 162 

Cracks  in 51 

Puffed  or  Swollen 32 

Salt  Glazing 64-68 

Drying,   Brick   Crack   in 161 

Stiff-Mud   Brick,    Break   in 167 

Losses  Caused  by  Improper  Tempering 160 

The  Effect  of  Artificial,  on  Clay 166 

Tile  Cracks  in 171 

Has    Trouble   with    Driep 161 

Dry  Pan  Capacity 170 

Duplicate    Equipment — Economy    of 176 

E 

Economy   of   Duplicate   Equipment 176 

Efflorescense  to  Locate  Source  of ........168-169 

To  Remove   from   Brickwork 124 

Electric  Power,  the  Cost  of ".'.""."".'.'.'.89-90 

Enamel  Brick 65 

Enameling,   Recipes  for  Black,   Blue   and  Green 65 

F 

Face  Brick  Absorption  Tests  on 134 

Burn   to   Full   Color   Range ...  50 

Burn    to    Too    Many    Shades ""  46 

Fire    Flashed 

Fan    Draft,    Substituting   Chimney   for    .  108 

Feathering  of  Clay  Bar "~140 

Fire   Brick  Dimensions 133 

Quantity   for   Kiln   Crowns 130 

Fire    Checks IS 

Fire  Clay  Calcining '.  Z!!l3t 

How   to  Keep  Coal   Out   of 93 

Methods  of  Washing ""  95 

Fire  Flashed  Face  Brick 

Flashed  Heads  on  Gray  Dry-Pressed  Brick 121 

Full    Color   Ranges    in    Face    Brick 50 


CONTENTS 


G 

Gas  Fuel,  the  Cost  of  Natural _ 88 

Glaze  (Blue)  for  Stoneware ~ 70 

Glazing  „    .  .  ....      61 

Salt    for _ 69 

Sewer  Pipe - ~ 61 

Under  Side  of  Kiln   Crowns _ .'..'.152 

With  Salt  In  Oil-fired  Kilns „ 74 

Green  Enamel  for  Enamel  Brick 65 

Greenish    Color    in    Sewer    Pipe _ 25 

H 

Harvard  Brick,  Imitations  of..._ 100 

Haulage   - _ _ 91 

Heat,  Controlling  Kiln  Temperatures _...  53 

Heating  Kiln  Bottoms „ _ „ 13 

Height  of  Kiln  Crowns _ _ 140 

Headers,  Imitations  of  Harvard „ _ 100 

Hollow  Tile,   Salt  Glazing...™ _ 63 

Discoloration  in   Painted  Walls  of 178 

I 

Imitations  of  Harvard  Headers _ 100 

Interior    Brickwork,    Mortar    Joints    for 98 

K 

Kilns,    Best   Height    for   Crowns 140 

Changing  Up-Draft  to  Down-Draft 54 

Claims    Has    New    Type _ 125 

Glazing  Under  Side  of  Crowns 152 

Proper  Size  of  Down-Draft...- _„ „ 49 

Proportionate  Kiln  and  Stack  Area „ 112 

Quantity  of  Fire  Brick  for  Crowns 130 

Salt  Glazing  in  Oil-flred ....  74 

Setting    _ _ 24 

To  Calcine  Fire-clay 131 

L 

Lamination   ....  79 

Lignite  Burning  in  Down-Draft  Kilns - 141 

Losses  Caused  by  Improper  Tempering „ 160 

Lubrication  85 

M 

Manganese  in  Connection  with  Shale 105 

Miscellaneous  -~ „ _ 87 

Molding  Sand,   Coloring  Matter  in 128 

Mortar   Color „ 101 

Mortar  Joints  for  Interior  Brickwork 98 

N 
Natural  Gas  Fuel,   the   Cost  of 88 

Off  Colored  Face   Brick ....  35 

Oil,  Comparative  Cost  of  Coal  and „ 155 

Oil  Fired  Kilns,  Salt  Glazing  in „ „ 74 

Overburned  Tops „ 24 

Oxide  of  Iron,  Adding  to  Produce  Red  Color""! ".!....117 

Patent  Office   Registration 97 

Power,  Electric,  the  Cost  of 89-90 

Varying   Motor   Loads   on    Shaft J51 


10  CONTENTS 


Preheating-   of    Plastic    Clay 15S 

Puffed   Drain   Tile 

Pyrometers  vs.    Cones 12'J 


Roo 


u ruing    S 
flng  Tile. 


Salt  for  Glazing 

Salt  Glazing.  Does  Not  Reach  Entire  Contents  of  Kiln- 
Drain  Tile 

Hollow   Building    Block 

In   Oil   Fired   Kilns 

Sewer  Pipe 

Sand-Lime  Brick,  Analysis  in  Manufacture 

Scum,  to  Locate  Source  of  Trouble 

To  Remove  from  Brickwork 

Setting  

Setting  Up-Draft  Kilns 

Sewer  Pipe,  Cement  Joints  in 

Greenish  Color  in 

Salt  Glazing  

Shafting,  Varying  Motor  Loads  on 

Shale,  Mixing  with  Surface  Clay 

Silica  Brick .'. 

Made   from    Silica    Sand 

Manufacture  of 

Silica  Sand 

Slag  Brick 

Slate  in  Brickmaking 

Slipping  of  Clay  Bar 

Soft-brick,  Kconomy  of  Ueburning 

Soft  Brick  in  Kiln  Centers 

Stacks,  Proportionate  Kiln  and  Stack  Area 

Steam  Lubrication  vs.  Water  Lubrication 

Steam  Shovels,  Using  in  Shallow  Work 

Stiff-Mud  Brick  Break  in  Drying 

Stoneware,  Blue  Glaze  for 

Stove  Lining  Cracks  in  Burning 

Swollen  Drain  Tile 

Swollen  or  Bloated  Brick 

Temperatures  

At    Which    Brick    Are    Burned '."."".'. 

At   Which   Manganese    Is    Fused 

Controlling    Heat    in    Down-Draft    Kilns 

Tempering  

Tile   Cracks    in   Drying 

Trade    Names,    Copyrighting 

Registering  

U 

Cnil'orm    Color   in   Face-Brick 4,; 

I'p-Draft  Kilns,   Changing  to   Down-Draft .".J..........  ""  :,4 

W 

Washing    Fire    Clay <,r, 

Water  Lubrication  vs.  Steam  Lubrication  ""  sr. 

Wet    Shale,    Difficulty    in    Grinding 17^ 

Whitewash,    to   Locate   Source   of   Trouble 168-169 

To   Remove   from   Brickwork 121 


CLAYWOKKIN'G    PROBLEMS 


CHAPTER  1 

WHICH  DEALS  WITH  BURNING 

Temperatures  at  Which   Brick  are   Burned 

5:10.  Pennsylvania— H'c  would  like  sonic  figures  giiing  us 
an  approximate  idea  of  the  temperatures  used  in  burning  brick 
c/  different  kinds. 

The  temperatures  at  which  various  kinds  of  brick  may  be 
considered  burned— that  is  finished — are  as  follows:  Com- 
mon brick  (red)  1,600  to  1,800°  F.  Paving  brick  or  shale 
vitrified  brick.  1,800  to  2,200°  F.  Face  brick  made  of  fire  clay, 
l.'.KK)  to  2.200°  F.  Fire  brick.  2.000  to  2.600°  F. 


Brick  Mash  in  Center  of  Kiln 

510.  Xorth  Carolina — MY  are  hating  trouble  with  some 
clay  we  are  working  and  we  thought  that  you,  or  some  of  your 
readers,  could  help  us.  Our  clay  is  hard  and  tough  in  the 
bank,  but  as  soon  as  it  is  dug,  and  the  air  gets  to  it  for  a  few 
hours,  it  pulverizes  and  works  through  an  auger  machine  as 
fine  as  we  could  expect,  the  brick  coming  through  the  dryer 
in  perfect  shape,  ll'e  are  using  a  25-ft.  down-draft  kiln  for 
burning.  In  the  center  and  bottom  of  the  kiln,  the  brick  mash 
and  fall  all  to  pieces,  just  about  as  lime  does  when  ivater  is 
added  to  it.  On  the  top  and  outside  of  the  kiln,  the  brick  vit- 
rify and  burn  as  hard  as  pig-iron. 

F.llis  Lovejoy,  C.  E.,  answering  the  above,  says: 

"I  cannot  determine  from  the  data  presented  the  cause  of 


CLAYWORKING    PROBLEMS 


the  trouble.  It  may  be  that  the  bond  is  so  weak  that  the  dry 
brick  crush  under  the  superimposed  weight.  It  may  be  due 
to  insufficient  draft  during  the  water  smoking  stage  in  con- 
nection with  too  rapid  water  smoking.  The  moisture  driven 
off  from  the  brick  in  the  upper  part  of  the  kiln  is  drawn  to 
the  bottom  of  the  kiln,  where  it  condenses  more  or  less  and 
softens  the  brick  in  the  bottom.  The  draft  of  the  kiln  should 
be  such  that  the  moisture  is  carried  away  as  rapidly  as  formed 
and  not  be  allowed  to  collect  in  the  bottom  of  the  kiln  and 
thereby  become  absorbed  by  the  bottom  brick.  It  may  be  that 
the  clay  contains  excessive  lime  and  if  the  water  smoking  is 
done  with  a  low  grade  of  coal,  high  in  sulphur,  there  will  be 
formed  in  the  kiln  considerable  sulphuric  acid  which  will  at- 
tack the  lime  in  the  clay  and  form  a  sulphate  of  lime,  the 
bulk  of  which  may  be  greater  than  the  original  lime  mineral 
and  the  expansion  due  to  this  increased  bulk  destroys  the 
bond  and  the  brick  crush  under  the  weight.  Sulphuric  acid 
readily  destroys  the  bond  in  clay  wares  and  even  though  there 
is  no  expansion  in  consequence  of  new  mineral  formations, 
the  bond  thus  weakened  may  be  insufficient  to  hold  up  under 
the  weight.  I  have  experienced  all  of  these  difficulties,  but 
the  second  above  mentioned  is  the  one  most  common." 

C.  S.  Kinnison,  of  the  Bureau  of  Standards,  Pittsburgh, 
Pa.,  gives  the  following  opinion  : 

"From  a  distance,  it  appears  that  your  trouble  is  due  to 
condensation  taking  place  in  the  kiln.  You  may  either  be 
setting  your  ware  too  wet  or  you  may  not  have  sufficient 
draft.  The  respective  remedies  are  apparent.  When  con- 
densation of  the  water  vapor  takes  place,  the  water  obviously 
trickles  down  through  the  ware  and  affects  the  courses 
towards  the  bottom,  worse  than  the  upper  ones.  The  result 
is,  that  they  become  so  wet  that  they  do  not  have  sufficient 
strength  to  carry  the  weight  imposed  upon  them  and  they 
crush.  You  might  also  try  allowing  the  clay  to  be  exposed 
to  the  weather  for  awhile.  There  is  a  remote  possibility  that 


CLAYWORKING    PROBLEMS  13 

your  clay  air-slakes  and  the  proce.     is  not  allowed  to  finish 
before  they  are  made  into  brick." 


Difficulty  in  Heating  Bottom  of  Kiln 

568.  Illinois— We  hare  trouble  getting  the  heat  to  the  bot- 
tom of  our  kilns,  partly  because  we  do  not  hai'e  good  draft, 
and  partly  because  our  bag  ii<alls  arc  high,  H'hy  is  it  that 
high  bag  walls  are  necessary?  Is  it  to  firerent  the  reducing 
flame  from  the  fire  hitting  the  clay  ware?  If  oxidizing  con- 
ditions could  pre^•ail  continuously,  which,  of  course,  is  im- 
possible, could  bag  walls  be  dispensed  with  entirely?  Would 
it  assist  us  to  lower  our  bag  walls  and  not  set  so  much  ware 
around  the  bagf 

See  the  answer  written  by  Ellis  Lovejoy  to  the  question 
immediately  preceding  this  (510  No.  Carolina). 

In  addition  to  this,  Otto  Pommer,  Quebec,  Canada,  of- 
fers the  following  as  his  solution  of  our  reader's  problem: 

In  order  to  get  the  heat  to  the  bottom  of  a  down-draft 
kiln,  I  would  strongly  advise  the  proper  manipulation  of  the 
dampers.  By  following  this  course,  I  have  never  had  any 
trouble  with  underburned  brick  at  the  bottom  of  the  kiln. 
Our  kilns  are  operated  in  the  following  manner : 

Watersmoking  is  carried  on  with  open  dampers  and  all 
the  draft  it  is  possible  to  get.  The  kiln  is  then  heated  up 
until  a  good  red  color  can  be  observed  through  the  upper 
peep  hole,  the  dampers  being  wide  open  while  this  is  being 
done.  The  dampers  are  then  closed  so  that  the  circulation 
of  air  in  the  kiln  is  very  nearly  at  a  standstill.  It  can  easily 
be  determined  when  this  stage  has  been  reached  by  observ- 
ing whether  there  is  any  movement  of  air  through  the  upper 
peep  hole.  Then  every  three  hours  I  open  the  dampers 
again  for  a  period  of  about  an  hour  to  bring  up  the  heat.  The 
firing  during  the  periods  between  the  opening  of  the  dampers 
must  not  be  quite  as  heavy  as  when  the  dampers  are  open. 


CLAYWORKING    PROBLEMS 


Continuing  with  this  procedure.  1  burn  down  cone  02  on  top 
of  the  kiln  and  cone  06  at  the  top  peep  hole,  and  nearly 
always  cone  011  or  010  two  courses  over  the  bottom.  When 
the  cones  are  down.  F  burn  for  six  hours  with  a  high  oxidiz- 
ing flame  to  remove  the  smoke  color  on  the  brick. 

I  am  using  high  bag  walls  and  do  not  consider  low  hag 
walls  of  any  assistance  in  getting  the  heat  to  the  bottom  of 
the  kiln :  a  high  wall  prevents  hremarko  on  the  brick  set 
around  the  bag  and  increases  the  capacity  of  the  kiln.  I 
cannot  imagine  a  condition  where  the  bag  walls  could  be 
disposed  of,  and  would  ask  you  what  would  become  of  the 
ware  placed  near  the  fire  boxes  and  how  would  the  ware  at 
the  top  of  the  kiln  be  burned?  Naturally,  the  fire  would  pull 
down  to  the  flue  in  the  bottom  of  the  kiln,  melting  the  lower 
courses  of  brick  and  leaving  the  ware  at  the  top  under- 
burned. 

I  would  advise  trying  the  method  we  are  using  and  leave 
your  bag  walls  as  they  are.  but  using  judgment  in  charging 
the  furnaces  when  the  dampers  are  lowered.  The  principle 
of  keeping  the  temperature  at  the  top  of  the  kiln  nearly  uni- 
form with  that  on  the  bottom,  is  becoming  widely  recognized 
as  the  best  method  of  burning.  I  am  using  a  pyrometer 
and  aim  to  keep  the  top  of  the  kiln  at  exactly  the  same  tem- 
perature as  the  bottom. 


Has  Bloated  Brick 

299.  Illinois— }Vc  make  an  end-cut  brick  using  a  J.  D.  Fate 
machine  and  hare  down-draft  kilns.  Sometimes  the  brick 
from  the  top  and  half  ways  down,  after  being  burnt,  are  round 
in  shape  and  some  people  tell  me  that  I  put  too  much  baking 
powder  in  them.  I  first  thought  it  was  because  of  setting  the 
brick  too  wet,  but  later  found  that  it  zvas  the  same  when  the 
brick  were  thoroughly  dried.  What  is  pnzzlimi  me  is  that  it 
only  happens  about  ei'ery  third  kiln. 

We  judge  that  he  is  up  against  black  coring  and  Moating. 


CLAYWORKING    PROBLEMS  13 

The  clay  probably  contains  carbon  or  sulphur  as  iron  pyrite, 
or  both.  If  the  clay  contains  carbon  and  the  latter  is  not 
burned  out  (oxidized)  at  a  low  red  heat,  the  gas  from  it  at 
a  high  heat  will  generate  faster  than  it  can  escape  and  in 
consequence  the  brick  is  bloated  by  the  expansion  of  the  gas. 
The  burned  brick  when  broken  will  show  a-  black  core  and 
have  a  spongy  appearance  (vesicular  structure)  due  to  the 
included  gas. 

The  baking  powder  illustration  given  is  a  very  apt  one. 
Just  as  the  baking  powder  in  biscuits  forms  a  gas  which,  in 
its  efforts  to  escape,  develops  pockets  which  gives  the  bis- 
cuit its  lightness  and  sponginess,  so  does  carbon  gas  act  in 
clay  ware.  It  is  a  common  trouble  and  easily  overcome  if 
the  carbon  is  not  in  too  great  excess. 

It  is  necessary  to  hold  the  kiln  at  a  low  red  heat  until  all 
the  carbon  is  burned  out.  This  can  be  determined  by  draw- 
ing tests  from  the  kiln  and  breaking  them.  It  is  only  safe 
to  advance  the  heat  when  the  dark  core  is  no  longer  seen  in 
the  test  brick. 

Iron  pyrite  (Fe  Si)  behaves  in  the  same  way.  Under  heat 
treatment  the  sulphide  breaks  up  and  sulphur  gas  (SO?) 
is  developed.  It  is  necessary  to  roast  out  the  sulphur  slowly 
in  order  to  give  it  a  chance  to  escape,  but  if  it  is  driven 
out  rapidly  after  the  pores  of  the  brick  have  been  greatly 
reduced  or  closed  by  shrinkage,  then  the  gas,  the  pressure 
of  which  is  increased  by  increasing  volume  and  by  the  ex- 
pansion due  to  the  advance  in  temperature,  will  bloat  the 
brick. 

Sulphur  is  not  so  easily  driven  off  as  carbon.  One  mole- 
cule comes  off  at  a  low  heat  but  the  last  molecule  does  not 
come  off  until  a  temperature  of  about  1,600°  F.  is  reached. 

Hold  the  kiln  at  a  low  red  heat  until  the  carbon  is  burned 
out  and  at  the  same  time  the  first  molecule  of  sulphur  will 
pass  off.  If  there  is  a  dangerous  amount  of  sulphide  present, 
it  will  show  as  a  saffron  core  in  the  test  brick  after  the  black 


16  CLAYWORKING    PROBLEMS 

carbon  core  is  burned  out.  Sulphur  in  large  amounts  is  also 
shown  by  excessive  blue  smoke.  If  there  is  such  excessive 
blue  smoke  then  after  the  carbon  is  off  the  heat  should  be 
advanced  by  stages.  Each  advance  will  start  off  more  sul- 
phur which  will  show  as  blue  smoke.  When  the  latter  be- 
comes light,  advance  the  heat,  and  thus  work  the  kiln  along 
until  the  blue  smoke  is  all  off  or  very  thin  and  until  it  does 
increase  with  advancing  heat,  then  the  kiln  may  be  finished 
off  in  the  usual  way  without  damage. 

If  the  clay  is  surface  material  the  chances  are  that  the 
trouble  is  due  to  carbon,  but  if  it  is  a  shale  or  a  deep  bedded 
clay,  the  trouble  may  be  carbon,  or  sulphur,  or  both. 

We  cannot  explain  why  every  third  kiln  has  this  trouble. 
We  are  not  superstitious  about  the  number  three,  nor  thir- 
teen, nor  twenty-three.  Several  years  ago  while  visiting  a 
plant,  after  presenting  our  card  and  explaining  our  busi- 
ness, the  superintendent  said  to  us,  "Come  with  me,  I  want 
to  show  you  something."  He  took  us  to  a  dry  press  ma- 
chine and  pointing  to  the  master  gear,  said :  "I  don't  know 
why  it  is,  but  that  wheel  breaks  every  Tuesday."  We  did 
not  know  why  that  wheel  should  always  break  on  Tuesday, 
nor  do  we  know  why  every  third  kiln  should  show  the  "bak- 
ing powder"  effect.  In  our  opinion,  it  just  happens  so. 

\Ve  referred  the  same  problem  to  another  expert  who  re- 
plies as  follows : 

"Baking  powder  has  the  reputation  of  being  quite  some 
bloat  producer,  and  your  troubles  in  this  respect  would  no 
doubt  be  ameliorated  if  the  quantity  of  said  baking  powder 
were  lessened  somewhat.  Seriously  speaking,  however,  we 
infer  that  the  "round"  brick  mentioned  are  brick  which  have 
bloated  or  bellied.  The  principal  cause  of  this  trouble  is  im- 
proper oxidation  of  the  carbon  contents  of  the  clay.  The 
failure  to  oxidize  the  carbon  in  clay  is  in  itself  not  so  harm- 
ful in  its  effect,  but  the  iron  content  is  thereby  changed  to  a 
condition  in  which  it  reacts  very  vigorously  with  the  silica  of 


CLAYWQRKING    PROBLEMS 17 

the  clay,  forming  compounds  known  as  ferrous-silicates,  which 
are  very  fusible,  or  have  low  melting  points,  k  is  evident  that 
the  carbon  in  a  brick  will  be  oxidized  first  on  the  surfaces, 
and  that  oxidation  will  be  slower  as  we  progress  towards  the 
center,  due  to  the  difficulty  of  the  necessary  air  reaching  it. 
When  insufficient  time  and  air  are  allowed  to  bring  about  the 
complete  combustion  of  the  carbon  in  the  brick,  we  are  con- 
fronted with  the  old  problem  of  "black-coring,"  the  outside 
of  the  brick  being  of  the  normal  red  color,  while  the  interior, 
or  the  core,  is  black  in  color,  due  to  the  presence  of  carbon. 
The  oxidation  period  is  arbitrarily  assumed  to  cover  the  tem- 
perature range  between  1,300°  F.  and  1,650°  F.,  and  the  kiln 
should  be  taken  up  rather  slowly  in  this  range  to  give  ample 
time  for  oxidation.  Draw  trials  will  of  course  show  when 
oxidation  is  complete  as  is  evidenced  by  the  disappearance  of 
the  black  core.  See  to  it  that  your  fires  are  oxidizing  during 
this  period,  by  keeping  open  grates,  etc.  If  insufficient  time 
is  allowed  during  this  period  and  the  kiln  is  taken  on  up, 
this  black  spongy  interior  melts  and  this  process  is  accom- 
panied by  the  evolution  of  gases  which  cause  the  brick  to 
swell  or  bloat,  leaving  a  space  between  the  core  and  the  out- 
side shell.  It  should  be  understood  that  if  the  clay  is  not  oxi- 
dized at  the  proper  time  it  never  will  be,  because  as  the  tem- 
perature rises  the  porosity  decreases,  and  the  composition 
of  the  fire  gases  becomes  less  and  less  oxidizing.  The  fact 
that  your  brick  are  end  cut  tends  to  make  oxidization  more 
difficult  because  it  can  be  seen  that  in  that  case  a  larger  per- 
centage of  the  surface  of  the  brick  has  been  in  contact  with 
the  die,  than  in  the  case  of  side  cut  brick,  and  the  result  is 
of  course  a  larger  percentage  of  smooth  surface,  through 
which  the  air  has  much  more  difficult  passage  than  through 
the  surface  made  by  the  cutting  wire.  You  experience  bloat- 
ing in  the  top  courses  because  the  top  gets  hot  quicker  than 
the  lower  part,  where  sufficient  time  elapses  to  bring  about 
proper  oxidization.  We  cannot  attribute  any  other  cause 


18  CLAYWORKING    PROBLEMS 


than  mere  chance,   as  an  explanation  of  the   fact  that  this 
difficulty  occurs  in  about  every  third  kiln." 


Believes  These  Are  Fire  Checks 

590.  Iowa— We  hare  before  taken  advantage  of  this  de- 
partment and  have  received  from  it  some  very  helpful  sugges- 
tions, so  we  arc  coming  back  again  to  see  if  we  cannot  find  a 
remedy  for  a  trouble  that  crops  up  in  the  course  of  our  burn- 
ing, or  rather  in  our  cooling  process.  The  trouble  is  nothing 
new  and  is  commonly  called  air-checking.  Our  method  of 
cooling  is  as  follows:  After  our  kilns  have  reached  the  maxi- 
mum temperature  of  approximately  2,100  degrees  F.  and  the 
last  fire  has  been  put  on,  the  kiln  is  allowed  to  drazv  into  the 
stack  for  a  period  of  one-half  hour  or  just  about  time  enough 
to  consume  all  of  the  coal  in  the  fire  boxes.  As  soon  as  the 
last  fire  is  burned  out,  the  fire  boxes  are  opened  wide,  the  six- 
teen openings  in  the  crown  of  the  kiln  are  pulled  back  two  or 
three  inches  and  the  damper  dropped  in  the  stack.  If  the  day 
is  windy  the  fire  doors  to  the  fire  boxes  are  closed,  as  soon 
as  the  fire  bags  commence  to  turn  a  little  dark.  And  all  of 
the  doors  arc  closed  within  from  two  to  fii'e  hours  after  the 
kiln  is  finished.  Iron  plates  are  set  up  in  the  openings  under 
the  grates,  which  leaves  very  little  space  for  any  air  to  be  ad- 
mitted to  the  kiln.  The  top  plates  arc  also  closed  within  two 
to  five  hours  after  finishing  the  kiln.  The  kiln  is  allowed  to 
stand  in  this  condition  for  forty-eight  hours  and  at  the  end 
of  that  time  the  door  is  taken  about  one-quarter  of  the  way 
away,  and  about  one-half  the  way  away  during  the  next 
twenty-four  hours.  The  following  twenty-four  hours  the 
doors  are  completely  taken  dozvn  and  the  grate  bars  are  taken 
from  the  fire  boxes.  The  sixteen  openings  on  the  top  of  the 
kiln  are  taken  off  and  the  kiln  is  open  as  much  as  it  is  pos- 
sible to  open  it. 

The  follotving  day  the  kiln  is  cool  enough  to  draw.   It  might 


CLAYWORKING    PROBLEMS 


be  well  to  add  that  the  biggest  part  of  our  air-checking  takes 
place  in  the  bottom  courses  of  the  kiln.  I  have  seen  instances 
where  every  pipe  from  12  inches  up  to  34  inches  would  be  air- 
checked  on  the  bottom,  while  the  top  courses  in  the  kiln  would 
be  good,  sound  pipe.  Another  peculiar  thing  is  that  we  may 
get  twenty  or  thirty  kilns  with  no  air-checking  at  all  and  then 
TCI'//  come  two  or  three  kilns  that  are  badly  air-checked. 

It  seems  to  me  that  the  checking  must  be  done  at  some 
stage  of  the  cooling  where  there  is  heat  enough  to  change 
the  nature  of  the  body  of  the  pipe,  and  my  reason  for  think- 
ing so  is  that  whenever  a  pipe  is  air-checked,  the  fracture 
shotvs  a  dense  glass-like  surface  and  yet,  if  you  break  the  same 
pipe  at  any  other  place  the  surface  is  rough  and  jagged. 

We  are  inclined  to  believe  that  the  cracks  are  not  air- 
checks  but,  on  the  contrary,  are  fire-checks.  If  this  asumption 
is  correct,  we  would  look  for  the  remedy  on  the  other  end  of 
the  burn,  or  during  the  watersmoking.  During  this  period 
strains  are  set  up  in  the  ware  (especially  in  the  larger  size 
pipe)  that  are  radically  different  from  strains  (and  consequent 
cracking)  that  occur  during  cooling.  Our  observations  are 
that  a  glazed  crack  is  a  product  of  the  watersmoking  period 
and  that  a  cooling  crack  is  rarely  glazed — that  it  has  the  same 
fracture  as  broken  cold  piece — except  for  color.  It  may  be 
caused  by  a  dirty  kiln  bottom  and  this  view  is  perhaps 
strengthened  by  the  statement  that  it  occurs  only  at  wide  in- 
tervals— one  in  twenty  or  thirty  kilns.  Dirty  flues  may  ob- 
struct or  alter  the  path  of  drying  gases,  and  the  ware  in 
some  sections  of  floor  may  not  be  thoroughly  dried  when  the 
heat  is  raised  and,  of  course,  is  in  a  prime  state  to  crack  when 
the  heat  finally  reaches  it.  We  do  not  believe  that  these 
checks  occur  during  the  burning  or  finishing,  inasmuch  as  you 
say  that  a  big  percentage  of  damaged  ware  is  on  or  near  the 
floor  of  the  kiln.  If  near  the  ring  or  batter,  then  it  might  be 
attributed  at  once  to  fluctuations  of  heat  in  furnaces,  but  a 


CLAYWORKING    PROBLEMS 


sufficient  fluctuation  to  injure  ware  on  bottom  is  hardly  pos- 
sible. 

.">',)().  /t'tc'c/ — /  bclicrc  yon  misinterpreted  my  statement  in 
regard  to  the  looks  of  the  fracture  on  «7w/  ttv  term  air- 
checked  pipe.  You  will  note  in  my  prcrious  letter  that  I  do 
not  use  the  term  "(/lazed"  in  referring  to  the  nature  of  the 
fracture  where  the  air-checking  occurs  but  I  do  say  that  this 
fracture  has  a  "glasslike"'  appearance.  U'e  get  some  of  ivhat 
you  term  fire-cracks  directly  in  front  of  our  fires  and  some- 
times in  the  top  courses  where  tlic  flames  strike  the  ware 
directly  in  front  of  the  bag-walls.  These  cracks  are,  of  course 
always  glazed.  Xow,  what  makes  me.  think  that  this  checking 
is  done  while  the  kiln  is  cooling  and,  at  the  same  time,  is  at  a 
temperature  of  from  850  to  1,000  degrees  Fahr.,  is  the  fact 
that,  if  I  draw  a  trial  piece  from  the  kiln  during  the  salting 
and  break  it  immediately,  it  will  show  a  glassy  surface  where 
it  is  broken.  This  would  lead  me  to  think  that  the  ware  is 
thoroughly  vitrified  but,  if  this  same  trial  piece,  which  I  hare 
already  broken,  is  allowed  to  cool  down  for  tw'o  or  three 
minutes  (or  until  it  is  perfectly  black)  and  is  again  broken, 
the  fracture  is  entirely  different  in  appearance  and  does  not 
resemble  a  piece  of  thoroughly  ritrified  pipe  in  the  least. 

Is  it  not  true  that,  if  our  checking  zvas  done  during  the 
water-smoking,  that  the  cracks  would  be  much  larger  than 
those  we  get  in  what  zvc  term  "air-checked"?  Air-checked 
pipe  hare  an  almost  inrisible  hairlike  check  that  runs  the  full 
length  of  the  pipe.  I  might  add,  for  your  information,  that 
we  do  not  touch  the  damper  after  it  has  been  dropped.  I 
would  like  to  cite  an  instance  of  how  hard  it  is  to  locate  the 
c.ract  cause  of  our  trouble.  We  hare,  next  to  our  stacks, 
what  is  called  a  back  draft  or,  in  other  zvords,  an  opening 
by  which  air  may  be  admitted  into  the  kiln  b\<  wav  of  the 
kiln  flues. 

This  is  done  by  dropping  the  stack  damper  and  pulling  off 
the  hack  draft  that  is  directly  aborc  the  stack  damper.  This 


CLAYWQRK1NG    PROBLEMS  21 

back  draft  has  aki'ays  been  left  off  after  the  stack  damper 
was  dropped.  We  started  to  work,  assuming  that  the  "air- 
checking"  as  we  term  it,  would  be  most  likely  to  occur  dur- 
ing that  stage  of  the  cooling  when  the  kiln  is  turning  from 
a  dark  red  to  a  black.  One  kiln  was  at  this  stage  of  the 
cooling  during  very  windy  weather  and  the  other  kiln  passed 
through  this  stage  of  the  cooling  during  fair  weather  and 
both  back  drafts  were  off.  Before  either  one  of  these  kilns 
were  drawn,  we  prophesied  that  the  one  which  had  the  back- 
draft  off  during  the  windy  weather  u'otild  be  the  one  that 
zcould  be  "air-checked"  and  the  other  would  not.  This  proved 
to  be  true  when  the  two  kilns  were  drawn  and  we  naturally 
supposed  that  what  had  been  causing  our  "air-checks"  was  the 
fact  that,  during  windy  weather,  the  cold  air  would  be  forced 
on  to  the  bottom  of  the  kiln  by  way  of  this  back  draft,  thus 
being  distributed  evenly  over  the  bottom  of  the  kilns  and 
causing  the  ware  to  be  uniformly  checked  throughout  the  en- 
tire bottom  courses. 

If  the  weather  was  fair,  and  no  wind  blowing,  the  open 
back  draft  would  not  be  a  dangerous  thing  consequently,  we 
proceeded  to  keep  this  back  draft  closed  at  all  stages  of  the 
cooling  and  hoped  to  thus  eliminate  any  possibility  of  a  con- 
stant influx  of  cold  air.  To  our  surprise,  however,  we  found 
in  the  kiln  that  we  drew  today,  which  happens  to  be  the  first 
kiln  in  which  this  new  method  of  cooling  has  been  tried,  the 
air-checks  are  worse  than  in  any  kiln  we  haz'e  drawn  for  a 
long  time. 

About  the  only  conditions  that  seem  to  remain  constant  is 
the  fact  that  this  trouble  nearly  always  follows  windy 
weather. 

Do  you  think  there  is  any  possible  chance  of  the  kiln  "air- 
checking"  during  the  time  it  cools  from  2,100  down  to  1,600 
degrees  Fahr.  provided  this  drop  in  temperature  is  distribut- 
ed over  a  period  of  si*  to  eight  hoursf 

Our  original  answer  to  your  question  was  based  on  your 


CLAYWORKING    PROBLEMS 


final  sentence  as  published  in  the  Dec.  1st  issue.  This  was. 
"the  fracture  shows  a  dense  glasslike  surface,  and  yet  if  you 
break  the  same  pipe  at  any  other  place,  the  surface  is  rough 
and  jagged." 

Our  use  of  the  word  "glazed"  shows  where  we  misinter- 
preted what  you  had  said  and  this,  we  trust  you  will  admit, 
is  a  very  natural  word  error,  "glasslike"  and  "glazed"  being 
similar  in  many  minds. 

In  your  second  letter  you  give  us  further  information  on 
the  point,  which  changes  our  opinion.  One  of  these  points 
is  where  you  say  "I  might  add  for  your  information,  that  we 
do  not  touch  the  damper  after  it  has  been  dropped." 

You  have  cleared  up,  in  your  second  letter,  the  point  of 
your  making  full  use  of  the  back  draft  through  the  damper 
manhole.  This  explanation  was  neglected  in  your  first  let- 
ter and  seems  to  indicate  the  road  to  safety  from  dunting  or 
air-checks.  Note  the  following  and  draw  your  own  conclu- 
sions before  you  study  ours  : 

Downdraft  cooling,  and  cooling  through  the  doors  and 
fire-boxes  by  means  of  stack  pull  will  cause  currents  of  cool- 
ing air  to  pass  down  through  the  ware,  following  the  lines 
of  least  resistance.  It  will  cause  cross  horixontal  currents  of 
air  and  result  in  a  lack  of  uniformity  in  cooling  which  in 
turn,  results  in  checked  ware. 

Heated  air  rises  naturally.  If  we  cool  by  up-draft  we  thus 
reverse  operations  in  a  most  natural  way. 

Given  the  above,  how  can  we  apply  it  so  as  to  produce  a 
lack  of  extreme  fluctuation  of  cooling  curve  and  compel  the 
cooling  advance  or  heat  retard  evenly,  over  the  entire  con- 
tents of  the  kiln? 

We  have  the  following  to  consider:  1 — back  draft  open- 
ing ;  2 — top  center  hole  and  sixteen  smaller  holes.  Upon 
the  proper  manipulation  of  these  two  variables  depends  tin- 
success  or  failure  of  the  cooling  operation. 

Operation  :     1 — drop  damper  in   stack   as   soon   as  coal  has 


CLAYWORKING    PROBLEMS  23 

burned  out  in  the  fire  boxes — in  your  case  in  one-half  an 
hour  after  finishing;  2 — mud  up  the  iron  plates  that  you  use 
around  the  fire  boxes  so  making  the  boxes  tight;  3 — open 
the  back  draft  hole  as  wide  as  you  wish  (it  has  nothing  to 
do  with  the  amount  of  the  intake  of  cold  air) ;  4 — open  up 
the  top  hole  and  all  other  auxiliary  crown  holes  slightly. 

The  heat  is  carried  upwards  by  the  air  that  is  evenly  de- 
livered over  the  bottom  of  the  kiln  through  the  perforations. 
The  amount  (or  volume)  and  its  uniformity  of  distribution 
over  the  entire  surface  of  the  floor  depends  on  the  pull 
erected  by  the  openings  at  the  top  of  the  kiln.  Start  cool- 
ing with  not  more  than  150  square  inches  of  total  top  holes 
—this  is  about  eight  square  inches  per  stack. 

The  result  is  that  the  bottom  ware  is  first  bathed  by  air 
that  comes  to  it  already  preheated  by  the  body  heat  of  the 
under-kiln  brickwork.  Depending  on  the  manipulation  of 
top  holes,  it  never  is  flushed  with  a  rush  of  cold  air  but  is 
cooled  gradually.  The  same  operation  takes  place  in  con- 
nection with  the  ware  directly  above,  and  so  on  to  the  top. 

The  doors  and  the  fire-boxes  are  opened  in  accordance 
with  your  past  experience. 

The  back  plate  cover  must  be  used  intelligently  in  windy 
weather. 

Answering  your  question  specifically  as  to  whether  we 
think  that  there  is  any  possible  chance  of  the  kiln  "air-check- 
ing" during  the  time  it  cools  from  2,100  down  to  1,600  de- 
grees—we do  not  feel  that  there  is  any  stated  time  during 
the  cooling  when  the  ware  will  or  will  not  check.  We  do 
think,  however,  that  it  is  most  liable  to  check  during  that 
period  when  the  ware  is  going  from  dark  red  to  black. 

Keep  the  bottoms  clean.  Dirty  flues  prevent  the  cooling 
air  from  circulating  and  so  cooling  evenly.  The  ware  that 


24  CLAYWORKING   PROBLEMS 


is  slighted  in  this  way  is  bound  to  suffer  when  the  kiln  is 
opened  wide. 


Has  Trouble  With  Top  Burns 

480.  lozva — We  arc  making  a  dryprcss  brick  and  arc  haz'- 
ing  sonic  trouble  in  getting  a  good  burn  on  the  upper  part  of 
the  kiln.  We  are  using  a  common  up-draft  kiln,  set  35  high. 
We  get  fair  to  good  brick  up  to  27  or  28  courses,  but  the  bal- 
ance of  the  top  courses  are  soft,  zvith  no  color,  and  haz'c  a 
ring  like  a  soda  cracker.  Is  there  anything  that  you  know 
which  would  help  us  out? 

The  brick  in  the  top  courses  in  your  kiln  are  undoubtedly 
set  too  far  apart,  allowing  the  heat  to  pass  through  the  kiln 
too  rapidly.  If  you  will  set  the  brick  in  your  top  courses  close- 
ly so  as  to  hold  the  heat  in  the  kiln  longer  you  will  undoubt- 
edly get  a  higher  percentage  in  the  top  of  your  kiln. 


Trouble  Seems  to  Be  With  Setting  and  Burning 

587.  Michigan — /  hare  recently  replaced  a  battery  of  up- 
draft  kilns  with  a  battery  of  rectangular  down-draft  kilns. 
Conditions  hare  reversed  tlictnselres  and  where  I  used  to 
get  soft,  unsalable  brick  on  top,  I  am  now  getting  oz'cr- 
burned  unsalable  brick,  zi.<hich  is  just  as  bad.  The  material 
used  should  stand  the  ordinary  heat  in  good  shape  but  the 
firemen  do  not  seem  to  be  able  to  control  the  variations  of 
temperature  in  the  horizontal  grate  furnaces.  I  am  sure  that 
our  difficulty  lies  here.  We  fire  once  each  thirty  minutes 
and  use  four  scoops  per  box.  Can  you  make  a  suggestion? 
We  will  be  glad  to  furnish  additional  information  if  it  is  re- 
quired. 

The  data  given  is  meager  but  in  order  lo  save  delay,  we 
submit  the  following  theories :  In  setting  the  brick  in  tip- 
draft  kilns,  you  probably  set  threc-on-one.  In  down-draft 


CLAYWORKING   PROBLEMS  23 

kilns  this  is  too  tight,  five-on-two  is  generally  good  practice. 
Also  along  this  line,  you  probably  neglect  to  give  the  setting 
u  good  angle  of  slope  on  heads  from  top  of  bag-walls  to  top 
of  setting.  Your  firing  charge  is  evidently  to  severe,  and 
four  scoops  per  box  each  half  hour  is  simply  waste,  unless 
the  amount  of  coal  on  each  scoop  is  small.  We  advocate 
the  absolute  elimination  of  "time  and  count"  firing.  In 
other  words,  do  not  fire  so  many  shovelfuls  of  coal  at  stated 
intervals,  but  fire  only  when  needed  and  then  only  as  much 
as  needed.  Fire  light  and  often,  spreading  the  charge  even- 
ly over  the  burning  coals.  Keep  the  bed  of  coals  thin  and 
watch  the  color  of  heat  on  the  bag-walls,  endeavoring  to  keep 
it  at  a  constant  color  and  avoid  a  white  incandescent  heat 
at  all  times.  Try  this  out  and  if  you  still  have  any  consid- 
erable percentage  of  over-burned  brick,  we  will  be  surprised. 


Has   Trouble   Burning   Sewer   Pipe 

146  Iowa — We  arc  using  a  fire-clay  for  the  manufacture 
of  sewer- pi f>c  and  drain-tile,  that  contains  a  considerable 
amount  of  Pyrites  of  iron  and  also  shows  a  small  percentage 
of  lime;  the  clay  is  ground  to  a  16  mesh  and  is  then  put 
through  the  usual  process  of  preparation.  When  the  ware  is 
put  in  the  kilns,  they  are  gii'cn  from  5  to  6  days  in  burning 
our  object  being  to  give  the  kilns  a  gradual  increase  in  tem- 
perature from  the  start  to  the  finishing  point,  which  t'arics 
from  cone  01  to  5;  this  i-ariation  may  seem  rather  queer,  but 
is  accounted  for  by  the  fact  that  if  we  finish  at  cone  01,  and 
keep  a  smoky  atmosphere  in  the  kilns,  we  can  get  fairly  good 
glaze,  but  the  pipe,  especially  the  larger  sices,  show  a  greenish 
color  which  is,  of  course,  undesirable.  Pipe  finished  under 
these  conditions  are  rery  smooth. 

We  hare  finished  kilns  at  cone  5,  maintaining  oxidising 
conditions  at  all  times  during  the  finishing  process,  and  trial 
pieces  drazvn  from  kilns  furnished  in  this  manner  show  a 
<i««d  bright  yluzc  and  the  ware  is  smooth;  but  2  hours  after 


CLAY  WORKING    PROBLEMS 


finishing,  this  bright  glaze  has  started  to  leave  and  continues 
to  get  duller  and  duller  until  at  the  end  of  12  or  14  hours,  the 
glaze  is  practically  dead.  If  we  burn  to  cone  5,  and  smoke  the 
kiln  intensely  between  the  salting,  we  get  a  much  heavier 
glaze  and  much  better  color,  but  the  ware  is  so  rough  that  it 
makes  it  almost  worthless  for  the  purpose  for  which  it  is  in- 
tended. 

}Vc  use  an  excellent  grade  of  Illinois  coal,  the  analysis  of 
which  shows  it  to  be  very  low  in  sulphur. 

What  we  would  like  to  know'  is:  Why  we  can  not  get  a 
bright  glaze  under  oxidizing  conditions  at  cone  5,  and  have 
our  ware  smooth  and  why  we  get  a  better  glaze  under  re- 
ducing conditions  without  having  a  rough  pipcf 

"Brick  and  Clay  Record"  referred  the  above  problem  to 
two  different  authorities  on  kiln  construction  and  burning, 
and,  since  the  opinions  they  give  are  somewhat  at  variance, 
\ve  publish  both;  the  first  is: 

By    Anton    Vogt,    Consulting    Engineer 

The  fireclays  generally  used  for  making  sewer-pipe  are  No. 
2  or  bastard  fireclay,  and  in  most  cases  contain  considerable 
pyrites  of  iron,  but  in  the  above  case  it  seems  that  by  grind- 
ing it  to  lf>  mesh,  the  pipe  should  not  get  rough  under  reduc- 
ing conditions  unless  some  coarse  particles  find  their  way 
into  the  wet  pan.  which  is  possible.  But  supposing  this  does 
not  occur,  then  the  fault  is  with  the  manipulation  of  the  draft, 
it  going  to  extremes,  and  in  one  case  too  much  oxidizing,  in 
the  other  too  much  reducing  takes  place.  There  is  a  happy 
medium  between  the  two  ways  and  this  cannot  be  supplied 
through  these  columns.  It  takes  a  practical  man,  who  has 
had  similar  experience,  to  be  on  the  ground  and  apply  his 
past  experience  and  knowledge  in  such  matters  and  learning 
the  existing  conditions  by  overseeing  the  burning  of  one  or 
more  kilns. 

This  correspondent  states  that  the  analysis  shows  a  small 
percentage  of  lime.  That  may  be  true,  as  far  as  the  sample 


CLAYWORK1NG    PROBLEMS  27 

that  was  analyzed  is  concerned.  We  know  that  clay  from 
the  same  mine  or  deposit  often  varies  in  the  different  stratas 
and  that  the  average  clay  used  for  the  manufacture  of  the 
pipe  may  have  considerable  more  lime  or  alkalies  in  other 
forms,  than  the  analysis  shows. 

The  same  is  true  with  coal;  the  analysis  may  show  a  small 
percentage  of  sulphur,  but  the  coal  that  is  used  on  the  kilns 
may  have  considerable  more,  even  if  coming  from  the  same 
mine.  It's  queer,  but,  nevertheless,  it's  a  fact. 

Why  the  man  in  trouble  cannot  get  a  bright  glaze,  a  heavy 
glaze,  under  oxidizing  conditions  with  a  higher  heat  cone  5, 
is  due  to  the  fact,  that  the  draft  in  the  kiln  at  the  time  of 
salting  is  so  strong  that  it  carries  most  of  the  soda  in  the  salt 
out  of  the  stack.  It  slips  off,  instead  of  playing  around  the 
pipe  to  deposit  the  soda,  uniting  with  the  silica  in  the  clay  of 
the  pipe's  surface  and  that  is  the  reason  why  he  cannot  get  a 
heavy  glaze  under  oxidizing  conditions. 

Why  he  can  get  a  heavier  glaze  under  reducing  conditions  is 
due  to  the  contrary  of  what  happens  under  oxidizing  condi- 
tions. The  vapors  remain  longer  in  the  kiln,  and  have  time  to 
form  the  glaze  and  a  heavier  glaze  is  produced  owing  to  the 
ware  in  the  kiln  being  flashed  more  under  reducing  conditions 
than  under  oxidizing  ones. 

"But,"  he  says,  "the  pipe  arc  rough  !" 

This  is  due  to  several  causes  and  no  man  can  correctly  de- 
fine the  cause  without  being  on  the  ground  to  investigate  the 
matter. 

By   Ellis   Lovejoy,   E.   M. 

The  three  conditions  mentioned  by  your  correspondent  are 
as  follows: 

(1)  Reducing  kiln  conditions  finishing  at  cone  01  produces 
a  fair  glaze,  smooth  surface,  with  greenish  color. 

(2)  Oxidizing   conditions    finishing    at    cone    5    develop    a 
bright  glaze  and  smooth  surface  but  the  glaze  soon  gets  dull 
after  exposure. 

(3)  Reducing  conditions  finishing  at  cone  5  result  in  bet- 


CLAYWORKING    PROBLEMS 


ter  color,  heavier  glaze,  but  'the  surfaces  are  very  rough 
(pimpled  with  iron-silicate  spots,  we  presume). 

We  will  discuss  these  in  the  above  order. 

A.— The  greenish  color  in  No.  1  is  due  to  a  combination 
of  the  lime  and  iron  to  form  a  lime-iron-silicate  which  is 
buff  to  green  to  black  in  color,  depending  upon  the  amount  of 
iron  present. 

Lime  in  clay  is  most  frequently  present  in  tl.e  form  of  a 
carbonate  (limestone)  which  under  heat  treatment  is  con- 
verted into  calcium  oxide,  which  we  know  as  "lime." 

In  this  form  it  can  readily  combine  with  other  compounds, 
provided  the  other  compounds  are  also  in  the  proper  state 
for  such  combination.  Iron  in  the  form  of  pyrite  is  a  sulphur 
compound.  Under  heat  the  sulphur  is  driven  off,  leaving  the 
black  oxide  which  combines  readily  with  other  compounds, 
but  if  we  have  oxidizing  conditions,  we  may  convert  the  black 
oxide  into  the  familiar  red  oxide  which  cannot  enter  into 
combination.  Now  under  the  conditions  mentioned  in  No.  1 
we  get  the  lime  and  iron  into  the  proper  form  and  combina- 
tion results  producing  the  characteristic  green  to  black  lime- 
iron  color. 

In  the  presence  of  sulphur  and  moisture  we  get  sulphuric 
acid  which  acts  on  any  lime  whatever  its  condition  to  form 
lime  sulphate.  In  water  smoking  the  kiln  we  have  sulphur 
from  the  fuel,  moisture  from  the  ware,  and  lime  in  the  ware, 
and  thus  we  easily  form  sulphate  of  lime,  or  it  may  be  that 
the  sulphate  is  already  in  the  clay  or  is  formed  in  the  process 
of  drying.  Under  reducing  conditions  this  sulphate  of  lime 
is  broken  up  and  when  broken  up  can  combine  with  the  iron 
since  in  decomposing  the  sulphate  we  get  the  oxide  as  above 
mentioned. 

Therefore,  under  reducing  kiln  conditions  it  matters  not 
whether  we  have  lime  carbonate,  oxide,  or  sulphate,  the  result 
in  the  end  is  the  same. 

Our  experience  is  that  salting  at  such  low  temperatures  dues 
not  give  a  bright  glaze  and  we  arc  of  the  opinion  that  a 


CLAYWOKKING    PROBLEMS  29 

better  glaze  will  develop  at  the  higher  cone.  We  do  not 
know  of  any  way  of  overcoming  the  green  color  produced 
in  No.  1  under  No.  1  conditions. 

B. — As  mentioned  in  "A,"  the  sulphate  of  lime  (common 
scum)  is  or  may  be  formed  in  the  ware  and  probably  ac- 
cumulates on  the  surface.  Under  oxidizing  conditions,  even 
at  temperatures  at  and  above  cone  5  this  sulphate  is  not 
broken  up  and  cannot  enter  into  combination.  It  remains 
on  the  surface  of  the  ware  and  prevents  the  fumes  of  the 
salt  from  coming  in  contact  with  the  clay  which  it  must  do 
to  get  the  necessary  silica  to  form  the  insoluble  glaze. 

Scummed  sewer  pipe  never  glazes  well  and  it  is  our  obser- 
vation that  the  glaze  on  scummed  pipe  soon  loses  its  lustre 
after  exposure  but  whether  due  to  instability  of  the  glaze 
through  lack  of  silica  or  to  some  chemical  reaction  between 
the  glaze  and  the  underlying  sulphate,  we  do  not  know. 

C. — Under  strongly  reducing  conditions  prevailing  in  the 
kiln  at  cone  5,  the  sulphate  of  lime  (scum)  is  broken  up  and 
the  conditions  are  the  same  as  in  "A." 

The  grains  of  iron  from  the  iron  pyrite  may  be  fully  re- 
duced but  are  not  dissolved  under  the  low  temperature  and 
time  of  No.  1  but  under  the  higher  temperatures,  the  grains 
enter  rapidly  into  combination  with  silica  to  form  an  iron 
silicate  which  fuses,  draws  up  into  globules,  and  when  near 
the  surface  of  the  ware,  the  globules  protrude,  forming  the 
black  pimples  so  common  in  many  sewer  pipe  products.  The 
lime,  of  course,  is  taking  up  its  share  of  the  iron  but  it  can- 
not absorb  the  larger  grains  of  iron  or  at  least  not  rapidly 
enough,  but  instead  we  have  the  grains  of  iron  taking  up 
silica  and  probably  also  lime  to  form  the  globules. 

At  low  temperatures  the  lime  acts  as  a  flux  and  predom- 
inates, while  the  grains  of  iron  are  largely  dormant,  but  at 
higher  temperatures  the  iron  becomes  the  predominating  flux 
locally  at  least  where  the  pimples  develop. 

The  amount  of  iron  in  these  globules  is  so  predominant 
over  the  lime  that  they  are  black  while  between  the  grains 


30 


CLAYWORKING    PROBLEMS 


of  iron  we  may  have  combinations  of  lime  and  iron  with 
the  green  color. 

We  do  not  understand  why  there  is  not  some  evidence 
of  the  green  color  unless  it  be  that  the  larger  development 
of  the  iron  at  the  higher  temperature  gives  a  general  darker 
color  and  mantles  the  green  color. 

It  seems  to  us  that  this  correspondent  must  choose  the  least 
of  the  evils  because  we  doubt  if  all  the  troubles  can  be  over- 
come in  the  burning. 

The  lime  content  complicates  the  problem. 

Where  the  trouble  in  rough  surfaces  is  due  simply  to  gran- 
ular iron  in  the  clay  which  would  be  the  physical  character 
of  the  iron  in  the  form  of  pyrite,  we  can  largely  overcome 
the  trouble  by  alternate  oxidizing  and  reducing  conditions.  It 
must  be  borne  in  mind  that  at  high  temperatures  even  under 
oxidizing  conditions,  oxidization  does  not  take  place,  but  rath- 
er there  is  some  reduction.  We  must  get  the  full  reduction 
at  low  temperatures.  By  the  alternating  treatment,  we  first 
reduce  some  of  the  iron,  and  this  is  oxidized,  perhaps  ab- 
sorbed, or  spread,  we  do  not  know.  Following  this  we  fur- 
ther reduce  and  again  oxidize,  and  in  this  way  completely  de- 
stroy the  grains  of  iron.  Whatever  the  explanation,  we  find 
by  this  treatment  that  the  rough  surfaces  are  greatly  lessened. 
In  the  presence  of  lime,  however,  the  iron  goes  into  combina- 
tion with  the  lime  and  the  green  color  is  produced.  Here 
we  have  a  choice  between  smooth  surfaces  and  green  color. 
It  will  be  remembered  that  during  the  reduction  periods  we 
are  at  the  same  time  reducing  the  sulphate  of  lime  and  in  the 
end  leave  the  surface  of  the  ware  to  take  the  full  glaze  de- 
sired. It  is  possible  that  the  increased  amount  of  iron  that  we 
get  into  general  distribution  and  combination  by  this  treat- 
ment gives  enough  darker  color  to  mantle  the  green  color 
from  the  lime  and  especially  might  this  be  true  if  the  lime 
content  is  small.  With  the  iron  thoroughly  scattered  and 
the  sulphate  of  lime  broken  up  and  dissolved,  we  may  finish 
the  burning  and  salting  at  a  high  temperature  which  develops 


CLAYWORKING    PROBLEMS  31 


the  bright  heavy  glaze  without  the  development  of  the  pimples. 

We  overcome  the  difficulty  entirely  in  the  burning. 

In  case  the  scum  is  formed  in  the  watersmoking  it  can 
be  prevented  by  watersmoking  with  wood.  To  get  the  scum 
we  must  have  sulphur,  moisture  and  lime. 

The  sulphur  comes  from  the  fuel,  the  moisture  from  the 
ware  and  the  lime  is  in  the  ware.  The  use  of  wood  elimi- 
nates the  sulphur  until  the  water  is  all  off.  and  then  we  may 
return  to  coal  firing  without  any  danger  of  scumming. 

If  the  ware  is  scummed  in  the  drying,  which  is  often  the 
case,  especially  if  crop  clays  are  used,  and  the  drying  is  very 
slow,  then  the  proper  course  would  be  to  treat  the  clay  with 
barium  carbonate  or  hydrate  to  break  up  and  precipitate  the 
lime  sulphate  so  it  cannot  escape  to  the  surface  during  the 
drying  period. 

After  this  question  and  reply  were  published,  another  re- 
ply was  received,  which  we  give : 

To  answer  your  question  fully  would  involve  a  complete 
discussion  of  burning  hollow  ware,  which  would  be  beyond 
the  province  of  a  department  like  "Questions  and  Answers." 

There  are  two  essentials  to  be  mentioned,  however,  in  this 
connection,  viz.,  (1)  regarding  time  allowed  for  oxidation, 
and  (2)  temperature  of  salting.  If  the  first  point  is  not 
handled  properly,  you  are  very  apt  to  find  trouble  in  the 
second. 

It  is  very  important  that  ample  time  be  given  for  oxidation. 
We  may  say  that  this  takes  place  between  about  1,200°  and 
1,600°  F.  Take  your  kiln  up  slowly  during  this  interval  and 
make  draw  trials  from  time  to  time,  in  order  to  observe  the 
elimination  of  the  black  core  in  the  center  of  the  trial.  When 
this  spot  disappears,  the  oxidation  can  be  considered  as  being 
completed.  It  should  be  borne  in  mind  that  oxidation  is  a 
process  which  requires  time  for  its  procedure,  as  well  as 
plenty  of  air. 

If  your  ware  is  not  properly  oxidized,  and  you  take  your 


CLAYWORKING   PROBLEMS 


kiln  on  up  too  soon,  you  are  quite  apt  to  have  indications  of 
a  bloated  and  over-fired  tile,  at  the  temperature  required  for 
salting.  We  are  of  the  opinion  that  you  probably  do  not 
allow  enough  time  for  oxidation  and  in  the  attempt  to  avoid 
an  apparently  over-fired  body,  a  temperature  sufficient  for 
salting  is  not  attained. 

Salt  glazing  is  an  operation  which  requires  a  fairly  high 
temperature  and  the  body  should  be  practically  mature. 

It  is  difficult  to  understand  why  you  cannot  obtain  dark 
ware.  It  would  seem  logical  that  as  the  percentage  of  shale 
was  increased  in  your  mixture,  the  color  would  darken.  In 
fact  if  you  reach  a  temperature  suitable  for  salting,  it  seems 
as  though  it  would  be  a  difficult  matter  to  avoid  dark  colors, 
using  shale  as  you  do. 

The  best  advice  we  can  offer  you,  however,  is  to  enlist  the 
service  of  some  expert  in  this  line  of  work. 


Tile  Puffs  in  Burning 

314.  Indiana — What  causes  drain  tile  to  szvcll  or  puff  in 
burning?  We  burn  our  tile  in  round  down-draft  kilns  and 
until  two  years  ago  used  wood  for  fuel  and  then  ice  seldom 
had  tiles  swell  and  had  a  good  burn  on  the  bottom  as  well 
as  the  top.  Since  using  coal,  we  seldom  get  a  kiln  burned 
flood  on  the  bottom  unless  we  hare  the  upper  lavers  swelled. 
Is  there  any  prcrentatire? 

Your  drain  tile  may  swell  in  burning  for  several  reasons, 
among  them  being,  setting  the  ware  wet,  black-coring  due 
to  imperfect  oxidation  and  finally,  overfiring.  There  should 
be  no  difficulty  in  determining  if  either  the  first  or  last  rea- 
son is  responsible,  and  the  remedy  is  of  course  apparent 
in  either  case.  If  the  second  cause  is  responsible,  it  will  be 
revealed  by  the  presence  of  a  black  core  in  the  center  of 
the  body  of  the  tile.  The  trouble  lies  in  the  fact  that  the  kiln 
is  taken  up  too  rapidly,  not  allowing  sufficient  time  for  oxi- 


CLAYWORKING    PROBLEMS  33 

dation  of  the  carbon  present.  As  the  temperature  increases, 
the  surface  of  the  ware,  of  course,  becomes  denser,  prevent- 
ing the  escape  of  the  gases  resulting  from  the  delayed  com- 
bustion of  the  carbon  which  brings  about  bloating.  The  rem- 
edy is  to  take  your  kiln  up  more  slowly  between  the  tem- 
peratures of  1,300°  F.  and  1,650°  F.  within  which  interval  the 
carbon  oxidizes.  Complete  oxidation  is,  of  course,  revealed 
by  the  disappearance  of  the  black  core,  as  shown  by  draw 
trials.  When  this  core  has  disappeared  the  kiln  can  be  taken 
up  at  the  usual  rate.  This  trouble  is  experienced  no  doubt 
in  the  top  courses,  because  in  a  down-draft  kiln  the  top  gets 
hot  first.  The  lower  courses  rising  in  temperature  more  slow- 
ly have  ample  time  for  complete  oxidation.  Wood  produces  a 
longer  flame  when  burning  than  does  coal,  and  this  gives  op- 
portunity for  the  kiln  to  heat  up  more  uniformly,  thus  avoid- 
ing the  trouble,  due  to  top  getting  hot  first.  This  is  a  prob- 
able explanation  of  the  fact  that  this  trouble  was  not  ex- 
perienced when  using  wood  as  a  fuel.  It  might  be  a  good 
idea  furthermore  to  change  the  flue  system  in  the  kiln  bottom 
somewhat  with  the  idea  of  getting  the  bottom  hotter.  See 
also  reply  to  299  Illinois. 


Use  of  Coal  Dust  in  Burning  Brick 

262.  Texas — Will  you  advise  me  fully  as  possible  as  to  the 
use  of  coal  dust  mixed  in  with  the  clay  it,  the  manufacture 
of  brick?  IV ill  it  open  up  tender  clay  that  is  subject  to  crack- 
ing? Will  it  make  harder  and  stronger  brick?  Does  it  assist 
any  in  burning?  Can  brick  so  mixed  be  burned  in  common 
updraft  kilns'  About  how  many  pounds  of  coal  dust  are 
used  per  1,000  brick?  Could  lignite  be  used  to  produce  the 
same  results  as  coal  dust? 

You  do  not  state  whether  you  are  making  your  brick  by 
the  soft  or  stiff  mud  process.  We  assume,  however,  that 
you  are  using  the  former  of  the  two.  If  the  brick  should 
happen  to  be  made  by  the  stiff  mud  process,  it  is  apparent 


CLAYWORKING   PROBLEMS 


that  difficulty  would  be  experienced  in  burning  out  the  coal 
added,  due  to  the  hindrance  offered  to  the  entrance  of  the 
air  into  the  brick  necessary  for  combustion.  If  the  clay  is 
very  plastic,  and  used  as  stiff  mud,  it  is  practically  impossible 
to  burn  out  the  dust.  No  special  difficulty  should  be  en- 
countered in  this  respect,  however,  if  the  brick  are  made 
of  soft  mud.  The  important  feature  in  burning  brick  con- 
taining coal  dust  is  that  plenty  of  time  be  given  for  a  slow 
complete  combustion  of  the  dust. 

Bituminous  coals  and  lignite  are  not  often  used  for  this 
purpose  because  of  the  volatile  matter  they  contain.  When 
the  coal  in  the  brick  reaches  the  ignition  point  the  evolution 
of  the  volatile  hydrocarbons  would  be  so  rapid  that  a  bloated 
brick  would  be  the  result.  Lignite,  being  lower  in  volatile 
matter  than  bituminous  coal,  is,  therefore,  preferable  to  the 
latter. 

For  this  reason,  viz.,  low  content  of  volatile  matter,  anthra- 
cite coals  are  most  frequently  employed  for  this  use. 

The  amount  added  varies  evidently  with  the  clay  used,  but 
probably  100  pounds  per  1.000  brick  represents  an  average 
figure. 

The  addition  of  coal  dust  would  undoubtedly  aid  in  the 
burning,  because  of  the  extra  heat  available  resulting  from 
its  combustion,  and  would  tend  to  make  the  brick  stronger 
and  harder.  No  difficulty  should  be  experienced  in  burning 
brick,  so  treated,  in  common  updraft  scove  kilns. 

If  the  clay  is  extremely  plastic  and  difficult  to  dry,  the 
addition  of  coal  dust  might  remedy  matters  somewhat,  but 
the  dust  cannot  be  considered  as  a  "leaning"  agent,  because, 
if  added  in  amounts  large  enough  to  play  this  role,  other 
difficulties  would  enter  as  a  result,  which  would  preclude  its 
use  in  this  .respect. 

There  are  just  two  clays  that  lend  themselves  to  the 
use  of  coal  dust  in  the  stiff  mud  process — the  Chicago  dis- 
trict clay  and  the  Hudson  river  clays.  The  Illinois  Brick 
Company,  for  instance,  uses  coal  dust  in  the  outside  courses 


CLAYWORKING    PROBLEMS 


to  hasten  burning.  These  are  common  brick,  however,  and 
the  resultant  rough  face  left  by  the  combustion  of  the  coal 
makes  little  difference. 


Diminishing  Flash 

383.  Ohio — We  are  making  a  high  grade  face  brick  from 
a  red  burning  shale  and  burn  with  coal  in  down-draft  kilns. 
The  to{>  eight  or  ten  courses  of  brick  have  a  flash  around  the 
edges  or  an  apparent  over-burn  and  the  brick  are  heavier  as 
ICY  near  the  top  courses.  While  these  make  a  I'ery  beautiful 
red  center  brick,  we  would  prefer  to  have  a  uniform  red  over 
the  entire  face.  What  could  I  do  to  oz'ercomc  or  even  dimin- 
ish this  flashf 

The  trouble  you  are  experiencing  in  the  top  eight  or  ten 
courses  is  due  to  reduction.  As  a  remedy  we  would  suggest 
that  in  your  fire  boxes  you  make  use  of  a  coking  plate.  This 
is  simply  an  iron  plate  on  which  the  coal  is  thrown,  where 
the  volatile  hydro-carbons  are  distilled  off  (coking)  and  the 
coal  (coke)  then  pushed  on  into  the  fire.  This  avoids  the 
periodic  reducing  conditions  apt  to  ensue  if  the  coal  is  thrown 
directly  into  the  fire,  where  the  hydro-carbons  distill  off  with 
a  "rush"  and  ignite.  The  coking  plate  brings  about  a  more 
uniform  combustion. 


Doby  Clay  Burns  Many  Colors 

340.  Arizona — In  burning  our  brick  this  summer  I  found 
that  there  were  a  few  in  each  kiln  which  were  very  near  the 
color  of  gold.  These  brick  were  near  the  fire  but  not  touch- 
ing it.  The  brick  are  supposed  to  burn  a  white  but  they  burn 
white,  blue  or  red,  according  to  the  distance  from  the  fire. 
tit'/A  o  few  golden  brick  mixed  in.  The  clay  used  is  a  red 
doby,  taken  from  the  top  of  the  ground  and  has  sulphur  and 
some  other  minerals  in  it.  The  kilns  used  are  the  open  ones 
of  which  the  casings  are  torn  down  after  the  kiln  is  burned. 


CLAYWORKING   PROBLEMS 


/  in'ish  to  ascertain  if  1  had  a  down-draft  kiln  could  I  burn 
a  brick  so  that  it  would  be  of  uniform  golden  color?  If  I 
should  send  a  sample  of  the  clay  and  a  fczv  brick,  could  you 
///TV  me  more  expert  adz-ice?  Do  you  knot*.'  of  any  brick 
t/iat  docs  burn  a  rich  yoldcn  color? 

From  the  information  given  we  would  say  that  the  color 
phenomena  shown  by  your  brick  when  burned  are  due  to 
"flashing."  Under  normal  conditions  of  burning,  the  brick 
develop  their  normal  color,  white — or  rather,  a  light  buff, 
we  presume.  This  color  is  developed  when  the  burn  is  made 
under  oxidizing  conditions.  The  reds  and  golden  yellows 
are  due  probably  to  "flashing,"  as  mentioned  above.  Flash- 
ing takes  place  when  oxidizing  conditions  are  followed  by 
conditions  strongly  reducing  and  this  in  turn  followed  by 
oxidation  during  cooling.  By  this  process  the  coloring 
qualities  of  the  iron  are  made  more  evident  and  various  color 
tones  are  produced  depending  upon  the  amount  of  iron  pres- 
ent and  the  nature  of  the  clay.  The  more  frequently  alter- 
nating oxidizing  and  reducing  conditions  are  brought  about 
the  more  easily  do  the  colors  develop.  The  blue  color  spoken 
of  is  due  no  doubt  to  strongly  reducing  conditions.  These 
brick  in  some  way  or  other  have  not  been  oxidized  follow- 
ing the  reduction  and  can  hardly  be  spoken  of  as  being 
flashed.  The  remedy,  of  course,  is  to  endeavor  to  avoid 
reducing  conditions  as  far  as  possible.  Keep  your  fires 
clean.  It  is  difficult  to  say  whether  or  not  your  brick  would 
develop  a  golden  yellow  color  if  burned  in  a  down-draft 
kiln.  Submit  your  sample  to  some  competent  expert  foi 
thorough  testing. 

There  are  any  number  of  clays  that  develop  a  color  on 
burning  similar  to  golden  yellow.  Most  any  No.  2  or  No.  S 
fire  clay  behaves  in  this  way.  Any  of  the  ceramic  depart- 
ments of  the  state  universities  will  make  the  tests  for  you 
for  a  nominal  fee.  They  would  require  about  1,500  pounds 
of  material  to  make  a  thorough  test.  Prof.  Paul  Teetor,  of 


CLAYWOKKING    PROBLEMS  37 

the  University  of  Kansas,  at  Lawrence,  Kans.,  has  a  most 
excellent  testing  laboratory,  and  is  nearest  to  you. 


Brick  Crack  in  Kiln 

459.  Texas — We  hand  you  herewith  an  analysis  of  our  clay, 
as  git  en  by  the  University  of  Texas.  We  arc  troubled  with 
our  brick  cracking  in  the  kiln,  seemingly  caused  b\  expan- 
sion during  hot  firing.  Crack  appearing  on  tu'o-inch  face 
of  brick  generally  about  the  middle  and  crack  running  towards 
center  of  brick.  It  also  seems  that  we  hare  not  enough  iron 
oxide,  or  coloring  agent  in  our  clay  to  give  our  ware  a  good 
red  color,  only  that  rvhich  is  exposed  to  intense  heat,  for  we 
are  getting  too  many  pale  brick  in  bottom  of  kilns  that  are 
burned  hard  enough,  but  haven't  the  color. 

We  would  like  to  know  if  there  is  any  chemical  or  mineral 
that  we  can  use  with  our  clay  acting  as  a  coloring  agent  with- 
out too  much  additional  expense  in  manufacturing.  We  are 
using  round  down-draft  kilns,  water  smoking  or  drying  with 
coal  and  finishing  with  oil. 

Please  adiise  us  as  to  handling  fires  and  time  we  should 
take  in  heating  up  kiln  and  burning.  At  present  we  are 
water  smoking  a  thirty-foot  kiln  containing  about  80,000  stiff- 
mud  brick  from  fire  to  six  days  and  finishing  kiln  in  about 
sixty  hours. 

What  effect  would  too  much  or  not  enough  air  going  into 
kiln  in  heating  up  period  hare  on  ~<.vare?    Any  information  or 
adiice  would  be  greatly  appreciated. 
The  analysis  is  as  follows : 
Contains  Dry  basis 

Silica 77.38 

Alumina ___ _ „....  13.33 

Oxide  of  Iron 3.27 

Hme „ _ .60 

Magnesia  .". ".".  ~""^~."V™.V"™"™~. J~™  None 

Carbonic  Acid „ „ _. None 

Sulphuric  Acid  None 

Loss  on   Ignition _ ."'......."..". .". 6.16 

100.74 
This   would   seem   to   indicate   that  it  is   a  variety  of   silt. 


38  CLAYWORKING    PROBLEMS 

The  cracking  difficulty  which  you  describe  is  explained  by 
the  extremely  high  silica  content.  It  is  a  well  known  fact 
that  silica  changes  into  another  form  at  about  900°  C.  (1652° 
F.)»  known  as  tridymite,  and  this  conversion  is  accompanied 
by  an  increase  in  volume.  It  follows,  therefore,  that  if  a 
clay  is  extremely  high  in  silica,  as  yours  is,  it  is  very  apt  to 
develop  cracks  when  heated  above  900°  C.  due  to  the  strains 
developed  by  the  increase  in  volume.  This  phenomenon  (the 
expansion)  is  inherent  in  the  material  itself  and  cannot  be 
eliminated.  However,  you  may  be  able  to  eliminate  the  cracks 
by  adding,  say.  25  per  cent  of  some  suitable  plastic  clay. 

The  percentage  of  iron  shown  in  the  analysis,  while  by  no 
means  high,  should  still  be  enough  to  produce  a  red  color 
in  burning,  provided  it  is  thoroughly  disseminated  through- 
out the  clay. 

It  would  not  be  practical  to  attempt  to  develop  a  suitable 
color  by  the  addition  of  some  colorant  like  ferric  oxide  be- 
cause of  the  impossibility  to  produce  the  necessary  dissemina- 
tion. 

You  can  probably  darken  your  brick  somewhat  by  firing 
with  reducing  conditions  or  deficiency  of  air. 

Unless  your  clay  is  extremely  tender,  the  period  of  water 
smoking  is  somewhat  lengthy.  Thirty-six  to  forty-eight  hours 
should  suffice  ordinarily. 

An  excess  of  air  in  firing  means  low  fuel  economy  because 
of  the  resultant  dilution  of  the  combustion  gases.  Any  ex- 
cess of  air  beyond  that  actually  needed  for  combustion  means 
an  increased  consumption  of  fuel  from  which  you  derive  no 
benefit. 

An  excess  of  air  would  have  no  effect  on  the  ware  other 
than  would  mere  oxidizing  conditions.  A  deficiency  in  the 
amount  of  air  used  implies  reducing  conditions,  which  as 
mentioned,  among  other  things,  would  tend  to  reduce  the 
iron,  giving  darker  colors. 

Ellis  Lovejoy,  E.  M.,  writes  : 

"The    analysis    which    you    give   is    open    to    question.      \Ye 


CLAYWORKING    PROBLEMS 


do  not  find  common  clays  without  some  alkali  and  if  we 
were  assured  the  analysis  was  correct,  we  would  advise  you 
not  to  use  the  clay  simply  because  it  would  be  very  difficult 
to  get  a  hard  burned  brick  from  such  a  material. 

The  clay  is  high  in  silica,  but  we  have  made  bricks  con- 
taining as  high  as  85%  silica. 

The  cracking  which  occurs  in  the  kiln  may  or  may  not 
be  due  to  the  burning.  Many  clays  crack  in  the  drying  but 
these  cracks  close  when  the  bricks  are  fully  dry  and  are  in- 
visible. In  burning  they  open,  and,  in  several  instances,  we 
have  found  that  the  cracking  which  was  attributed  to  the 
burning  really  occurred  in  the  drying. 

If  the  trouble  is  in  the  drying  there  will  be  many  broken 
bricks  in  tossing  and  setting,  due  to  deep  cracks,  and,  if 
there  is  such  loss,  then,  unquestionably,  many  more  cracked 
bricks  which  withstand  the  handling,  find  their  way  into  the 
kiln. 

The  cracks  may  be  due  to  the  burning  and  largely  be- 
cause the  clay  is  high  in  silica  and  especially  will  this  be 
true  if  the  silica  is  very  fine  grained  (silty). 

It  occasionally  happens  that  the  cracking  is  due  to  the 
cooling  and  this  is  especially  true  in  highly  silicious,  silty 
clays  which  burn  to  a  very  dense,  almost  glassy,  body.  Cracks 
due  to  the  cooling  can  easily  be  determined  because  they  do 
not  open  up  and,  in  fact,  are  not  visible.  When  such  bricks, 
however,  are  struck  together,  the  evidence  of  a  crack  becomes 
apparent  and  when  broken  the  depth  of  the  crack  is  dis- 
covered. 

If  there  is  very  little  dryer  loss  and  if  the  cracks,  after  the 
bricks  are  burned,  are  more  or  less  open,  then  it  is  likely 
that  the  trouble  occurs  in  the  burning.  Cracking  in  the  burn- 
ing is  difficult  to  overcome,  but  some  improvement  will  result 
through  slower  burning. 

It  is  evident  from  the  analysis  that  there  is  not  sufficient 
iron  to  give  a  deep  red  color.  We  have  tried  powdered  iron 
ore  and  it  is  frequently  recommended  as  an  addition  to  the 


40  CLAYWORKING    PROBLEMS 

clay  lacking  in  iron,  but  our  experience  with  the  use  of  iron 
ore  has  not  satisfied  us  that  it  is  a  desirable  addition.  It 
will  give  a  darker  color  to  the  brick,  but  the  color  is  a  dull, 
lifeless,  brownish  red  and  very  unsatisfactory.  In  sand  mold- 
ed bricks,  we  have  on  several  occasions,  recommended  wet- 
ting the  sand  with  a  solution  of  ferrous  sulphate  (copperas), 
followed  by  drying.  This  treatment  of  the  sand  produces  a 
brilliant  red  color  and  this  method  of  coloring  the  sand  for 
sand  molded  bricks  is  in  practical  use. 

It  has  often  occurred  to  us  that  ferrous  sulphate  might  be 
used  in  the  same  way  to  intensify  the  red  color  of  burned 
clay,  especially  where  the  clay  is  highly  silicious,  as  in  this 
instance.  It  would  involve  wetting  the  dry  clay  with  a  solu- 
tion of  ferrous  sulphate  and  then  drying  it  thoroughly  in 
order  to  oxidize  the  sulphate.  This  treatment  will  leave  every 
grain  of  the  clay  mass  coated  with  a  red  stain  which  burns 
to  a  brilliant  red.  This,  so  far  as  we  know,  has  never  been 
tried  out  and  the  objection  has  been  raised  to  it  that  the  sul- 
phate so  introduced  would  greatly  increase  the  scumming, 
which,  theoretically,  would  be  true,  but  in  our  experience 
theory  and  practice  do  not  always  agree. 

In  regard  to  the  time  of  heating  up,  this  depends  upon 
the  character  of  the  clay  and  can  only  be  properly  deter- 
mined by  experimental  work  on  the  yard.  If  the  bricks  are 
dry  when  set  in  the  kilns  and  are  not  too  dense  (which  would 
be  unlikely  in  this  sandy  clay),  there  is  little  danger  in  ad- 
vancing the  fires  rapidly  in  the  early  stages  of  the  burning. 
The  only  moisture  present  is  the  hygroscopic  water,  and  this 
can  only  be  driven  off  by  temperatures  above  the  boiling  point 
and  by  the  heat  entering  into  the  clay  mass.  Ordinary  dry- 
ing is  from  the  surface  and  the  water  is  brought  to  the  sur- 
face by  capillarity,  by  hygro-scopic  water  does  not  come  to  the 
surface  by  capillarity  and  must  be  evaporated  by  heat  in  con- 
tact with  the  surface  of  the  grains  of  the  clay,  or  sand,  hold- 
ing the  moisture  by  surface  tension.  The  amount  of  moisture 
is  necessarily  small  and  there  could  not  be  sufficient  steam 


CLAYWORKING    PROBLEMS  4t 

developed  at  the  rate  at  which  the  heat  will  penetrate  the 
brick  to  cause  any  rupture  of  the  bond.  We  hold  that  in 
such  instances  it  is  generally  safe  to  advance  the  heat  rap- 
idly in  the  early  stages  of  the  burning,  or  what  is  known  as 
the  watersmoking  period. 

Oxidation  begins  at  a  low  red  heat  and  at  this  tempera- 
ture or  slightly  lower  (800°  to  900°  F.)  the  combined  water 
in  the  clay  is  coming  off  and  we  recommend  that  the  fir- 
ing be  not  loo  rapid  during  this  stage.  The  clayworkers 
whose  material  is  high  in  carbon  and  sulphur  are  fully  ac- 
quainted with  the  necessity  of  slow  firing  during  this  oxi- 
dation period,  and  they  have  an  excellent  guide  in  the  black 
core,  due  to  the  carbon  and  know  that  it  is  only  safe  to 
advance  the  fires  after  this  black  core  has  fully  disappeared. 

Clays  which  do  not  contain  carbon  or  sulphur  are  not 
troubled  with  the  black  coring  and  its  resultant  bloating 
and  in  consequence  there  is  no  evidence  that  the  burning 
may  not  progress  rapidly  during  this  oxidation  period,  but  it 
is  our  opinion  that  we  should  go  slow  during  this  stage 
whether  we  have  a  high  carbon  content  or  not.  It  has  been 
proven  conclusively  that  in  some  clays,  at  least,  there  is  a 
marked  expansion  during  this  oxidation  period,  or,  rather, 
during  the  period  when  the  combined  water  is  being  driven 
off,  which  is  coincident  with  the  early  stages  of  oxidation. 
A  highly  silicious  brick  which  naturally  would  have  a  weak 
bond,  under  the  strains  due  to  this  expansion,  would  be  very 
likely  to  crack  and  slower  advance  of  the  heat  during  this 
period  will  give  the  clay  mass  greater  opportunity  to  adjust 
itself  to  the  strains  introduced. 

Beyond  the  oxidation  period  we  have  found  it  usually  safe 
lo  advance  the  heat  rapidly  until  the  maximum  temperature 
in  the  upper  part  of  the  kiln  is  attained.  Then  our  practice 
is  to  check  the  draft  and  reduce  the  firing  and  under  this 
condition,  hold  the  kiln  until  the  heat  has  reached  the  bottom. 

It  is  impossible  to  say  how  many  hours  or  days  should  be 
consumed  in  wartersmoking,  in  the  oxidation,  in  advancing 


CLAYWORKING    PROBLEMS 


the  heat  to  the  maximum  temperature,  and  in  the  final  soak- 
ing heat.  Some  clays  can  be  burned  without  damage  from 
start  to  finish  in  from  four  to  five  days  for  bricks,  and  much 
shorter  time  in  drain  tile  and  hollow  ware.  Other  clays  will 
require  fourteen  to  fifteen  days  for  bricks.  From  seven  to 
nine  days  for  a  complete  burn  is  common  practice. 

The  fires  should  be  light,  but  gradually  increasing  during 
the  watersmoking,  but  when  the  oxidation  period  is  reached 
there  should  be  no  increase  in  the  fires  until  the  oxidation  is 
complete,  following  which  the  fires  can  be  advanced  as  rapid- 
ly as  practical  until  the  maximum  temperature  Js  attained, 
when  again  the  fires  should  be  checked  commensurate  with 
checking  the  draft.  During  the  water  smoking  and  oxidation 
the  damper  should  be  wide  open  with  the  greatest  possible 
draft  attainable  and  a  large  excess  of  free  air.  Following 
the  oxidation  the  air  supply  should  be  reduced  to  a  minimum 
in  order  to  get  economy  of  fuel.  The  amount  of  air  which 
may  be  admitted  during  the  latter  stages  of  the  burning  de- 
pends largely  upon  the  results  desired.  If  dark  flashed  colors 
are  sought,  then  the  fires  must  be  heavy  with  a  minimum 
quantity  of  air,  but  if  clear  red  colors  are  wanted,  there  must 
be  some  excess  of  air  going  through  the  fires  to  avoid  flash- 
ing." 


Cracks  in  Stove  Lining  Burns 

264.  Vermont— We  hai'e  had  some  trouble  at  a  fire  brick 
plant  in  which  we  are  interested  and  which  largely  manu- 
factures stove  linings.  The  trouble  is  that  the  brick  keep 
coining  out  cracked.  The  cracks  usually  are  someivhcre  on  the 
edge  of  the  brick,  about  midway,  and  run  dozvn  toward  the 
center  for  about  one  to  tzvo  inches.  We  hare  been  unable  to 
remedy  this.  W e  are  using  practically  the  same  clay,  the 
same  kilns,  and  the  same  men,  in  producing  the  goods  as 
u-e  hare  heretofore.  ]]'c  cannot  find  that  these  cracks  appear 


CLAYWOKKING    PROBLEMS  43 

more  often  in  brick  from  one  part  of  the  kiln  than  from  any 
other.  If  you  can  gii-e  us  any  ad^ice  that  will  help  us  to 
right  this  matter  we  will  much  appreciate  it. 

Several  explanations  may  be  given  for  cracks  appearing  in 
the  stove  lining  upon  being  burned.  It  is  understood,  of 
course,  that  cracks  may  develop  from  either  an  excessive 
shrinkage  or  expansion.  One  or  several  of  the  following 
explanations  may  fit  your  case : 

(1)  Although  the  clay  you  are  now  using  may  come  from 
the   same   deposit   as   that   used   in   the   manufacture   of   the 
brick   which   did  not  show   cracking,  it  still  may  vary  con- 
siderably   in  composition    from   the   latter.     In   this   instance 
your  clay  is   probably  too   silicious,   which   causes   excessive 
expansion  of  the  brick  when  burned,  which  results  in  crack- 
ing. 

(2)  You  may  not  be  using  enough  plastic.     Increase  the 
amount  of  bond  clay. 

(3)  In  case  you  are  using  a  flint  fire  clay  in  the  manu- 
facture of  the  lining,  try  using  a  smaller  amount,  replacing 
it  with  ground  bats,  or  calcine  the  flint  clay  before  using  it. 
Too  much  flint  clay  may  cause  cracks  due  to  high  shrinkage. 

(4)  Careless  molding  may  be  responsible,  as  a  result  of 
sand  cracks,  etc. 

(5)  Probably  you  are  not  drying  the  brick  uniformly  all 
over.    Try  turning  them  sooner. 

It  should  be  stated,  that  in  cases  of  this  kind,  the  clays  or 
the  mixture  of  clays  used,  should  be  given. 


Fuel   Changes   Color   of   Dry   Press   Brick 

43.  Missouri — We  are  making  a  dry-press  brick  from  a 
blue  to  brown  shale,  and  are  having  a  hard  time  to  get  them 
red  enough  for  a  good  face-brick.  When  we  burned  them 
with  natural  gas,  we  did  very  well,  but  since  we  have  used 
wood  and  coal,  the  brick  burn  to  a  yellowish  color.  In  all 


CLAYWORKING    PROBLEMS 


other  respects  the  brick  are  good  and  solid,  but  the  color  is 
bad.  We  burn  in  tip-draft  kilns,  thirty-eight  brick  high.  The 
top  fifteen  courses  come  out  light  red  and  salmon  colored. 
Those  in  the  arches  and  paving  bench  are  all  right,  and  hard 
burned.  We  would  like  to  know  if  we  can  burn  these  brick 
in  a  continuous  tunnel  kiln,  three  hundred  feet  long,  twelve 
feet  wide  and  ten  feet  high,  with  four  roivs  of  pot  holes  on 
top.  Chestnut  coal  would  be  burned  and  a  fan  be  used  for 
draft.  We  do  not  care  to  go  in  much  for  making  face-brick. 
ll'hat  we  do  want  to  get  is  a  good,  hard  common-brick.  We 
can  change  to  the  stiff  mud  process,  and  want  a  kiln  that  will 
burn  the  brick  hard  from  top  to  bottom.  If  you  do  not  think 
that  the  continuous  kiln  is  suitable  for  our  ware,  what  kind 
of  a  kiln  would  you  recommend?  Do  you  think  that  mixing 
clay  with  the  shale  would  make  the  brick  redder? 

Red  color  in  clay  wares  is  due  to  iron,  and  it  should  make 
no  difference  whether  the  burning  is  done  with  gas,  wood  or 
coal,  provided  proper  conditions  are  maintained  in  the  fur- 
naces. 

There  are  many  clays  and  shales  that  contain  lime,  not 
necessarily  lime  pehbles  but  constituent  lime  which  can  only 
be  detected  by  a  chemical  'test.  Now,  a  limey  clay  or  shale 
may  contain  sufficient  iron  to  give  a  red  color  when  burned, 
but  in  the  presence  of  lime,  the  iron  combines  with  the  lime, 
and  the  color  of  the  burned  ware  may  be  buff  instead  of 
red.  It  may  be  possible  to  burn  either  pale  red  or  buff,  and  if 
''Missouri's''  clay  or  shale  contains  lime,  the  different  color 
effect  may  be  due  to  the  firing.  The  iron  cannot  combine 
with  the  lime  without  being  reduced.  If  in  firing  with  gas 
he  kept  an  oxidizing  condition  in  the  kiln,  the  product  would 
have  been  red  until  a  very  high  temperature  was  obtained 
when  reduction  would  take  place  whether  there  was  excess 
of  air  present  or  not. 

In  firing  with  wood  or  coal,  he  may  get  reducing  condi- 
tions at  much  lower  temperatures  than  with  the  gas,  when 


CLAYWQKK1NG    PROBLEMS  45 

the  color  "turned  to  buff.  The  fact  that  he  gets  pale  reds  in 
the  top  of  the  updraft  kiln  is  indicative  of  the  presence  of 
lime,  if  the  lower  brick  are  buff.  Oxidizing  conditions  pre- 
vailed in  the  upper  part  of  the  kiln,  and  the  temperature 
was  not  high  enough  to  reduce  *the  iron  and  combine  it  with 
the  lime,  hence  the  brick  had  a  red  color. 

If  the  shale  is  not  limey,  it  may  be  that  the  discoloration 
is  due  to  scumming,  but  this  is  so  well  known  to  brick- 
makers  "that  it  certainly  would  have  been  recognized.  The 
top  brick  too  would  be  as  liable  to  scumming  as  in  any  other 
part  of  the  kiln.  If  the  trouble  is  scum  it  may  be  accounted 
for  by  the  sulphur  gas  from  the  coal,  which  might  cause  the 
scum,  whereas  the  natural  gas  would  not  give  this  'trouble  in 
so  far  as  it  might  be  due  to  the  sulphur  from  the  fuel.  Dry 
press  brick  are  not  seriously  troubled  with  scum  and  we  do 
not  think  this  can  be  the  trouble.  We,  in  this  instance,  are 
inclined  to  suspect  lime. 

He  can  undoubtedly  burn  the  brick  in  a  tunnel  continuous 
kiln  using  nut  coal  for  firing,  and  get  an  all  hard  product. 

The  continuous  kiln  will  give  a  different  color  effect  "than 
the  updrafts  if  the  clay  contains  lime.  It  may  give  more  red 
color  but  the  chances  are  that  the  red  will  not  be  uniform. 

Sulphur  gas  is  accumulative  in  a  continuous  kiln  and  is 
converted  into  sulphuric  acid  in  wa*tersmoking  sections  of 
the  kiln.  The  acid  attacks  the  lime  and  converts  it  into  sul- 
phate. Sulphate  of  lime  is  not  easily  reduced  and  in  con- 
sequence does  not  combine  so  readily  with  the  iron,  thus  leav- 
ing the  iron  free  to  produce  a  red  color.  However,  "the 
practical  result  is  not  a  uniform  red,  but  a  streaked  red  and 
buff,  which  is  not  as  satisfactory  as  either  the  pale  reds  or 
the  usual  limey  buffs. 

The  continuous  kiln  will  use  very  little  fuel  and  burn 
all  hard  brick,  which  makes  it  a  satisfactory  kiln  for  common 
brick,  especially  in  districts  where  fuel  is  high. 

We  cannot  tell  what  effect  the  clay  would  have  upon  the 


4<i  CLAYWORKING   PROBLEMS 


color — it  all  depends  upon   whether  the  clay  alone  burns  a 
redder  color  than  'the  shale. 


Has  Trouble   Getting   Uniform   Burns 

99.  Alinnesota — We  haz'c  ventured  into  the  face  brick  busi- 
ness and  experience  some  trouble  in  getting  .the  right  color. 
Our  clay  will  have  a  yellow  or  buff  color  at  2,000  degrees  F. 
zvhen  we  get  the  heat  to  2,200  F.  the  clay  vitrifies  and  gets  cr 
dark  brown  or  black  color  and  the  brick  will  have  a  glaze 
similar  to  a  salt  glaze.  Nozv,  if  we  could  be  able  to  get  the 
same  result  every  time  we  would  be  pleased,  but  sometimes  the 
burn  will  get  a  yellowish  green  and  sometimes  the  dark  brown 
or  almost  black.  Now,  I  wish  that  some  of  your  readers 
would  put  me  on  a  way  to  get  the  dark  effect  every  time.  How 
is  a  reducing  fire  handled  so  as  to  get  a  dark  color  every 
time  on  the  ware?  We  are  burning  in  down-draft  kilns,  a 
coking  table  fire-box  is  attached  zvith  grates;  kilns  are  30  ft. 
in  diameter.  I  should  like  to  hear  through  your  z'aluable  col- 
umns or  by  nnil,  and  would  appreciate  an  ansz^er  very  much. 

Our  correspondent  undoubtedly  is  dealing  with  a  limey 
clay  which  largely  predominates  in  the  northwest,  particularly 
Wisconsin  and  Minnesota.  These  clays  contain  both  lime  and 
iron  and  the  color  result  from  'the  kiln  is  a  battle  royal  be- 
tween the  lime  and  the  iron. 

The  matter  that  surprises  us  is  that  he  can  burn  these 
clays  to  vitrification  in  any  quantity  in  a  commercial  kiln. 
A  Ifttle  lime  does  no  harm.  A  certain  amount  of  lime  af- 
fects the  burning  range  very  seriously  and  such  clays  have 
such  a  short  burning  range  that  they  are  very  difficult  to 
burn  let  alone  vitrify.  While  lime  acts  as  a  flux  through 
a  range  of  temperatures,  it  is  not  very  active  un'til  a  cer- 
tain critical  temperature  is  reached,  then  it  acts  quickly 
and  to  the  full  amount  in  the  clay  with  'the  result  that  a 
brick  made  of  limey  clay  passes  quickly  from  a  soft  prod- 
uct to  a  fused  pasty  mass,  and  this  fusion  point  is  where 


CLAYWORKING    PROBLEMS  47 


vitrification  begins  and  instead  of  a  vitrified  product  we  have 
a  swelled  spongy  mass. 

When  lime  is  in  excess  (we  have  seen  bricks  made  from 
clays  containing  more  than  30  per  cent  lime),  it  being 
refractory  and  in  such  excess  that  it  cannot  flux  with  the 
clay  mass  in  sufficient  quantity  to  soften  the  entire  mass, 
the  product  is  a  soft  brick  even  at  temperatures  far  in  excess 
of  commercial  kiln  heats. 

To  return  to  the  question  of  color:  The  red  color  of 
a  brick  is  due  to  iron  in  the  clay  and  as  the  temperature 
increases  the  red  gets  darker  and  darker. 

So  long  as  the  color  is  red,  the  iron  is  not  in  combina- 
tion with  the  clay,  and  the  burned  clay  is  simply  colored 
with  the  naturally  red  oxide  of  iron.  When  the  iron  be- 
gins to  combine  with  the  clay,  dark  iron  alumina  sili- 
cates form  which,  when  all  the  iron  is  absorbed,  or  rather 
in  fusion,  if  the  latter,  is  in  sufficient  quantity,  may  be 
black.  All  are  familiar  with  the  iron  spot  bricks  in  which 
the  black  iron  spots  are  simply  iron  silicates. 

When  an  entire  brick  approaches  an  iron  spot  condition 
it  may  be  black.  As  the  iron  passes  from  the  free  red 
colored  s*tate  into  the  fused  condition,  the  brick  changes 
from  a  red  to  a  brown  increasing  in  darkness  until  the 
black  is  reached  if  there  be  sufficient  iron. 

Iron  in  the  red  (ferric  oxide)  state  cannot  enter  into 
combination  and  it  first  must  be  reduced  to  ferrous  ox- 
ide and  for  this  reason  when  we  wish  to  make  gun  metal 
bricks  we  must  have,  at  least  part  of  the  time,  a  reducing 
condition  in  the  kiln — a  condition  in  which  the  gases  of 
combustion  not  being  able  to  get  oxygen  in  sufficient  quan- 
trty  from  the  air  admitted  through  the  furnaces  will  take  it 
from  any  oxide  minerals  in  the  clay  and  thus  these  oxides 
are  reduced  and  the  remaining  mineral  put  in  condition  to 
combine  with  silica,  etc. 

Lime    introduces    another    condition.     The    lime   combines 


CLAYWORKING    PROBLEMS 


with  silica  even  more  readily  than  iron  especially  under 
oxidizing  conditions  and  as  soon  as  the  lime  begins  to 
combine  it  takes  up  some  of  the  iron,  more  and,  more 
as  the  heat  advances,  and  a  lime  iron  silica  is  formed.  The 
color  of  a  limey  brick  which  also  contains  iron  will  be 
pale  red  at  a  low  heat  (soft  brick)  passing  into  a  buff,  a 
greenish  buff,  a  green,  to  a  dark  green,  even  a  greenish  black 
if  the  percentage  of  iron  is  high. 

What  our  correspondent  wishes  to  do  is  to  ge't  the  ef- 
fect of  the  iron  under  reducing  conditions  without  hav- 
ing it  mantled  by  the  effect  of  the  line.  We  doubt  if  it 
can  be  done.  One  would  think  tha't  it  might  be  possible 
to  maintain  a  strongly  oxidizing  condition  in  the  kiln  which 
would  prevent  the  absorption  of  the  iron  but  not  of  the 
lime  and  when  the  lime  had  been  taken  up,  'that  by  a  sud- 
den and  strongly  oxidizing  condition  the  iron  might  be  sent 
into  combination  without  being  completely  mantled  by  the 
lime,  but  we  doubt  it.  The  lime  silicate  formed  during  'the 
oxidizing  fire  would  be  more  greedy  for  the  iron  than  any 
free  silica  and  we  get  the  green  lime  iron  silicate  instead 
of  the  black  iron  silicate. 

We  are  inclined  to  think  that  the  variation  in  color 
which  he  ge'ts  is  largely  due  to  variations  in  the  content 
of  iron  and  lime  in  the  clay.  When  iron  predominates, 
the  black  color  will  prevail,  and  when  lime  is  the  more 
prominent  mineral,  he  will  get  the  green.  So  delicate 
is  the  balance  between  these  two  minerals  and  so  sensitive 
are  combinations  of  them  to  changes  in  temperatures  and 
kiln  conditions,  that  we  do  not  believe  he  can  control  the 
color  in  such  a  crude  furnace  as  a  brick  kiln. 

There  are  three  ways  in  getting  reducing  conditions  in 
a  kiln  and  each  gives  a  different  color  effect.  One  way  is 
to  fire  with  clear  open-fires  up  to  within  a  few  hours  of  the 
finish  of  the  burn,  then  change  to  a  reducing  fire  (smoky). 
Another  way  is  to  fire  several  hours  oxidizing  alternating 


CLAYWORKING    PROBLEMS  49 


wfth  several  hours  reducing  throughout  the  burn,  ending  with 
a  reducing  fire. 

Another  method  is  to  fire  with  a  smoky  flame  and  weak 
draft  throughout  the  burn  to  within  a  few  hours  of  the 
finish  and  then  to  top  off  with  as  strongly  reducing  condi- 
tion as  possible  yet  a*t  the  same  time  have  as  strong  draft 
as  possible. 

We  have  seen  some  remarkable  effects  from  burning 
with  choked  draft  and  incidentally  it  may  be  mentioned  that 
it  greatly  tends  to  bring  out  the  colorific  power  of  iron. 
We  have  no  idea  what  effect  ft  would  have  on  a  lime  iron  clay. 


Proper  Size  of  Down  Draft  Kilns 

167.  Tennessee — We  icould  be  pleased  to  have  opinions  as 
to  the  most  successful  and  economical  sice  of  round  down- 
draft  kilns  for  burning  fire  clay.  Is  a  kiln  of  30  ft.  inside 
diameter  as  good  as  one  of  26  ft.f 

Years  ago  sewer  pipe  manufacturers  built  their  kilns  20 
to  24  ft.  in  diameter,  then  26  to  28  and  30  ft.  In  recent  years 
they  have  been  building  them  32,  34,  36  and  40  ft.  diameter. 
A  40  ft.  is  the  limit  for  the  reason  that  if  built  larger  it 
would  necessitate  going  higher  with  the  crown,  and  that 
would  not  be  practical,  as  it  gives  too  much  space  above  the 
ware  and  if  crown  were  not  built  according  to  the  size  of 
the  kiln,  it  naturally  would  be  too  flat,  the  result  of  which 
would  be  that  it  would  not  last  long. 

Covering  the  question  of  economy  of  kilns,  the  large  kilns 
are  more  economical  as  to  capacity  and  fuel  consumption, 
provided  that  the  bottom  of  kiln  is  of  such  construction  that 
the  heat  is  distributed  to  all  parts  of  the  kiln,  uniformly,  to 
the  center  and  door  ways,  as  well  as  to  the  sides. 

As  to  capacity,  take  for  instance,  that  a  26  ft.  kiln  has  an 
area  of  530.93  square  feet;  a  36  ft.  kiln  has  approximately 


50  CLAY  WORKING    PROBLEMS 


twice    as    much    area,    or    1,017.9    square    feet,    consequently, 
double  the  capacity  of  a  26  ft.  kiln. 

In  proportion  to  capacity  the  larger  kilns  are  cheaper  to 
build  than  the  smaller  ones,  and  the  fuel  consumption  in  pro- 
portion is  less.  For  kilns  where  ware  at  high  temperature, 
such  as  fire  brick  and  also  flashed  brick  are  burned,  the  28 
to  30  ft.  size  is  recommended,  especially  for  sewer  pipe,  tile, 
fireproofing  and  other  hollow  ware,  as  well  as  for  common 
brick,  this  size  being  the  most  economical.  For  paving  brick 
and  face  brick  the  smaller  size  gives  better  results. 


To  Secure  Full  Color  Ranges 

.'543.  Mississippi — Will  you  kindly  inform  me  as  to  the  ma- 
terials or  chemicals  that  are  used  in  connection  with  the  burn- 
ing of  brick  under  reducing  conditions,  to  secure  full  raric- 
f/atcd  color  effects,  noiv  so  popular? 

The  so-called  ''pea-cocks"  and  other  variegated  colors  now 
so  popular  in  burned  brick  are  obtained  simply  by  virtue  of 
reducing  conditions.  The  colors  obtained  vary  with  the  in- 
tensity of  the  reduction  and  the  period  of  time  during  which 
these  conditions  are  maintained.  There  are  various  means 
used  for  intensifying  the  reducing  conditions,  the  most  effec- 
tive and  probably  the  most  common  one  being  ordinary  tar. 
Toward  the  end  of  the  burn  the  liquid  tar  is  introduced  into 
the  kiln  through  openings  in  the  crown.  Only  a  relatively 
small  amount  is  used  and  it  is  introduced  slowly  by  drip- 
ping from  a  suitable  vessel.  This  operation  is  continued  for 
about  an  hour  or  so  or  until  the  tar  has  been  completely 
broken  up  and  the  kiln  is  filled  with  strongly  reducing  gases. 
It  is  essential  that  these  conditions  be  maintained  only 
a  rather  short  period  of  time  if  the  variegated  color  effects 
are  desired.  When  the  conditions  are  reducing  for  only  a 
brief  period  it  is  evident  that  only  the  edges  and  exposed 


CLAYWORKING    PROBLEMS 


faces  of  the  brick  will  be  affected,  producing  variegated  colors 
in  the  brick.  If,  however,  the  kiln  atmosphere  is  held  re- 
ducing for  a  considerable  length  of  time,  the  entire  surface 
of  the  brick  will  experience  reduction  by  virtue  of  the  in- 
crease in  time  and  there  is  a  tendency  for  the  brick  to  assume 
a  more  or  less  uniform  color  which  is  undesirable  in  this  par- 
ticular case. 

At  the  present  time  the  production  of  the  beautiful  "pea- 
cock" colors  seems  not  to  be  under  control  and  very  few  are 
obtained  from  a  kiln.  It  would  seem  very  possible,  how- 
ever, that  if  some  simple  systematic  researches  were  carried 
on,  it  would  be  found  that  the  development  of  this  color 
could  be  brought  under  a  much  closer  control  than  now 
exists. 

Some  of  the  crude  oil  by-products  can  be  used  for  this 
purpose  also.  Their  action  is  somewhat  different  from  that 
of  the  tar,  the  resulting  colors  being  somewhat  less  intense 
than  when  the  latter  is  used.  In  using  either  material  the 
kiln  is  kept  tightly  closed  and  the  same  care  taken  to  main- 
tain reducing  conditions  by  the  manipulation  of  the  fires  as 
would  be  the  case  under  ordinary  reducing  conditions. 

It  should  be  stated  that,  by  a  proper  handling  of  the  fires, 
the  same  color  effects  can  be  obtained  merely  by  the  use  of 
coal  alone,  no  tar  or  other  similar  material  being  used.  It 
is  simply  a  question  of  attaining  extremely  reducing  condi- 
tions. 


Big  Tile  Crack  Lengthwise 

46.  Utah — /  made  some  4,  5  and  6-inch  drain  tile  to  try 
my  clay.  The  4  and  5-inch  tile  are  good  and  there  is  not 
much  lost  by  cracking,  but  about  one-third  of  the  6-inch  tile 
cracked  lengthu"ise.  I  burned  them  in  an  up-right  kiln  and 
•'stuffed"  the  6-inch  Zinth  4-inch.  I  want  to  know  why  the  6- 
inch  tile  cracked,  while  the  others  did  not.  Would  the  stuff- 


CLAYWORKIXG    PROBLEMS 


ing  make  any  difference/1  I  was  just  as  careful  in  making 
and  drying  one  as  the  other,  and  all  were  made  on  the -same 
pattern  of  die. 

Stuffing  tile  makes  a  decided  difference.  A  number  of 
manufacturers  of  drain  tile  have  learned  that  they  can  burn 
their  tile  with  very  little  loss  when  it  is  set  single,  but  when 
they  attempt  to  "stuff"  the  smaller  tile  in  the  larger  the  loss 
in  the  larger  tile  becomes  excessive. 

This  is  not  true  of  all  clays,  but  it  is  true  of  some,  and  to 
this  may  be  clue  the  trouble  your  correspondent  is  having. 

The  trouble  may  also  be  due  to  the  die.  It  is  remarkable 
how  sensitive  some  clays  are  to  the  slightest  differences  in 
manufacture.  The  dies  may  be  the  same  character,  and  yet 
the  tile  of  one  si/e  may  crack  and  another  not.  Manufac- 
turers of  fireproofing  who  have  tender  clays  are  fully  a\vare 
of  troubles  which  arise  from  very  slight  changes  in  the  char- 
acter of  the  clay  or  in  the  die. 

The  straight  line  crack  in  drain  tile  is  primarily  due  to 
the  bridge  in  the  die  which  cuts  the  column  into  two  streams 
and  these  two  streams  do  not  knit  firmly  together  again. 
Now  suppose  we  have  a  tender  clay,  in  a  small  tile,  greater 
pressure  is  required  to  force  the  clay  through  the  die  and  this 
greater  pressure  may  be  sufficient  to  bond  together  the  two 
streams  flowing  into  the  die  so  they  will  withstand  the  drying 
and  burning  strains.  A  larger  tile  may  be  weak  because  of 
the  lighter  pressure. 

The  smaller  the  die  the  more  heat  there  is  generated  in 
forcing  the  clay  through  it.  A  small  die  will  get  hotter  than 
a  large  one.  This  heat  will  raise  the  temperature  of  the  wa- 
ter in  the  clay,  and  this  effect  alone  may  suffice  to  bond  the 
smaller  sizes  while  the  larger  sizes  are  just  weak  enough  to 
crack  under  the  drying  strains. 

We  do  not  know  what  the  cause  of  the  trouble  in  the  Utah 


CLAYWORKING    PROBLEMS 


plant  may  be,  and  merely  mention  the  above  facts  to  show  how 
very  slight  differences  may  be  the  cause  of  the  trouble. 

We  have  known  instances  where  simply  turning  a  perfectly 
symmetrical  die  upside  down  overcame  cracking. 

We  would  suggest  that  your  Utah  correspondent  first  try 
burning  without  "stuffing"  and  if  this  does  not  overcome  the 
trouble  then  he  should  investigate  the  die  conditions. 


Cannot  Raise  Heat  in  His  Kilns 

666.  lozva — 7  hare  two  round  down-draft  kilns  which  I  hare 
burned  once.  They  \\ave  ofen  fire  boxes — that  is  they  hare 
no  grates.  They  hare  large  -flues  connected  to  a  fifty  foot 
stack  ivhich  stands  between  the  two  kilns  and  which  is  only 
about  jiV  feet  away  from  them.  We  are  using  "Enterprise" 
lump  coal,  which  is  mined  in  Iowa  and  which  burns  good  in 
all  other  styles  of  round  kilns,  and  I  hare  never  before  had 
trouble  in  raising  the  required  heat — that  is  until  I  tried  burn- 
ing the  two  kilns  which  I  hare  mentioned.  We  seem  to  hare 
an  abundance  of  draft  and  the  fires  roar  until  you  can  hear 
them  for  quite  a  distance.  These  are  new  kilns  for  me  and  I 
may  not  be  handling  them  correctly.  I  saw  in  a  recent  is- 
sue of  "Brick  and  Clay  Record"  an  answ'cr  to  one  of  your  cor- 
respondents who  wanted  to  know  about  open  fire  kilns  and  I 
tried  checking  the  draft  as  suggested  in  your  answer  to  him. 
irhcn  I  did  that,  howerer,  the  coal  would  not  burn.  We  set 
the  brick  cross-way  in  benches  three  brick  wide  and  hare  a 
two-inch  flue  from  top  to  bottom  between  erery  bench.  Is 
this  the  right  way?  I  burned  these  two  kilns  for  five  days 
after  the  water-smoke  was  off  and  eren  then  the  face-brick 
were  very  soft,  and  there  was  only  a  medium  burn  on  the  com- 
mon-brick. Can  you  answer  me  by  letter  and  give  me  some 
pointers  about  the  proper  plan  to  handle  this  style  of  kiln? 
The  main  trouble  is  that  I  cannot  get  the  kilns  hot. 

The  probabilities  are  that  the  opening  into  the  furnace 
above  the  bed  of  coals  is  too  large  and  the  bed  of  coals  too 


CLAYWORK1NG    PROBLEMS 


thick.  This  would  cause  a  surplus  of  cold  air  to  be  drawn 
into  the  kiln  over  the  fires  instead  of  through  the  bed  of  coals 
as  this  air  will,  of  course,  follow  the  path  of  least  resistance. 
The  remedy  is  to  keep  the  fires  clean  and  to  keep  the  bed 
of  coals  as  thin  as  consistent,  firing  light  and  often,  also  to 
provide  a  smaller  opening  in  the  opening  over  the  fire,  by 
banking  the  coal  higher.  This  permits  the  furnace  to 
"breathe"  or  draw  the  air  through  the  bed  of  coals  and  this 
supports  combustion.  It  may  be  possible  that  in  this  process 
the  furnace  will  become  too  hot  and  this  must  be  regulated 
by  the  amount  of  fuel  and  frequency  of  fire  as  well  as  by  the 
size  of  the  opening  over  the  fires.  Regarding  the  setting- 
do  not  set  with  a  two-inch  flue  between  the  benches  but  set 
the  benches  tight  together  and  set  the  brick  "five  on  two." 
Do  not  set  too  high  in  the  kiln  but  leave  three  to  four  (or 
more)  feet  between  the  top  of  the  setting  and  the  kiln  crown. 
The  reply  given  to  "651  Illinois"  in  the  April  20  issue  of 
"Brick  and  Clay  Record"  has  evidently  been  read  by  the  cor- 
respondent whose  question  we  are  now  attempting  to  answer. 
We  recommend  that  he  read  that  reply  again,  particularly  para- 
graphs (A),  (B)  and  (C)  and  not  to  lose  faith  in  the 
methods  suggested  there  on  account  of  one  unfortunate  ex- 
perience. The  chances  are  that  the  draft  was  cut  too  much 
and  went,  of  course,  to  the  opposite  extreme.  The  draft 
should  be  of  such  strength  that  the  fuel  burns  freely,  but  the 
fires  should  never  "roar." 


Wants  to  Change  System  of  Burning 

667.  Utah — We  are  planning  a  change  in  our  system  of 
burning  and  expect  to  build  down-draft  kilns  to  take  the  place 
of  our  present  equipment,  which  is  up-draft.  We  manufac- 
ture both  zarire-cut  and  dry-press  brick  and  farm  drain  tile. 
In  our  nezv  equipment  ive  will,  in  all  probability,  include  ma- 
chinery for  the  manufacture  of  hollow  building  blocks.  Will 
you  refer  its  to  someone  who  designs  a  kiln  that  would  take 
care  of  our  products  and  give  satisfactory  results?  We  arc 


CLAYWOKKING    PROBLEMS 


somewhat  impressed  with  the  picture  of  the  kiln  and  the 
methods  of  bracing  which  appeared  in  your  issue  of  April  6 
on  page  654.  //  was  marked  "Figure  15."  Can  you  tell  us  at 
whose  plant  this  kiln  is  located  so  that  we  can  take  the  mat- 
ter up  with  the  owners  and  see  what  success  they  have  had 
regarding  even  burns  on  this  style  of  kiln?  Any  other  infor- 
mation regarding  the  erection  of  a  kiln  to  wit  our  purposes 
will  be  greatly  appreciated. 

Considering  the  fact  that  you  will  use  your  kilns  for  the 
making  of  several  very  different  kinds  of  ware,  we  believe 
you  will  get  better  results  by  using  round  down-draft  kilns 
than  those  of  the  rectangular  type.  This  question  has  been 
the  subject  of  controversy  for  a  great  many  years  but  we  be- 
lieve we  are  warranted  in  making  the  statement  that  where 
the  same  kiln  is  to  be  used  for  burning  more  than  one  kind 
of  material,  better  results  are  obtained  in  the  round  type  than 
in  the  rectangular.  The  round  down-draft  kiln  does  not  hold 
as  many  brick  as  the  rectangular  kiln  does  but  the  cost  of 
up-keep  is  less  and  the  results  somewhat  more  exact.  The 
type  of  flue  and  method  of  draft  in  any  kind  of  kiln  tha't  may 
be  adopted  will,  to  a  large  extent,  determine  what  percentage 
of  ware  you  can  get  out  of  the  kiln.  At  the  same  time,  the 
floor  that  would  be  suited  for  burning  brick  (which  needs 
sanding)  might  not  be  especially  adapted  for  the  continuous 
burning  of  hollow  ware,  without  making  some  provision  for 
the  proper  setting  of  the  latter— a  provision  which  would 
have  to  be  made  each  time  the  kiln  was  turned. 

The  care  with  which  a  kiln  is  built  has  a  great  deal  to  do 
with  its  results  and  if  the  walls  are  not  properly  constructed 
and  bonded  and  braced,  the  life  of  the  kiln  will  be  short  and 
the  condition  of  the  burned  ware  not  so  satisfactory  as  it 
would  be  if  the  kiln  were  correctly  built.  The  encasing  of 
kiln  walls  on  a  round  type  of  kiln  by  a  steel  shell  extending 
from  the  top  to  the  bottom  of  a  kiln  is  one  way  of  insuring 
against  the  loss  of  heat  through  radiation — a  condition  which 
is  increased  by  the  cracks  in  the  kiln  walls,  due,  frequently, 


CLAYWORKING   PROBLEMS 


to  bad  construction.  Our  investigation  has  proved  this  type 
of  construction  to  have  a  great  deal  of  merit  and  the  steel 
shell  kiln  is  confidently  recommended  to  our  correspondent's 
attention. 

The  kind  of  fuel  which  you  will  burn  and  the  requisite  area 
of  grate  surface,  the  size  and  the  height  of  stack,  should  be 
gone  into  very  carefully  before  you  finally  decide  upon  the 
fundamentals  of  your  new  construction. 

The  Fredonia  Brick  Company  of  Fredonia,  Kansas,  which 
makes  face-brick  and  wire-cut  commons  is  now  changing  over 
to  down-draft  kilns  and  these  are  all  round  kilns.  Why  not 
write  to  some  of  the  men  or  firms  that  make  a  specialty  of 
kiln  building  and  whose  advertisements  appear  in  the  columns 
of  this  magazine? 

Regarding  the  rectangular  kiln  which  is  shown  in  the  article 
published  in  our  April  6  issue,  we  suggest  that  you  write 
direct  to  Profession  Harrop  at  the  Ohio  State  University, 
Columbus,  Ohio,  who  has  this  information. 


Wants  Advice  on  Setting  Up-Draft  Kilns 

6'.  2.  Pennsylvania — /  atn  writing  you  to  get  v&ur  best  ad- 
vice on  a  condition  which  gives  us  a  great  deal  of  loss  and 
annoyance.  We  make  a  line  of  common,  red  building  brick, 
known  to  the  trade  as  "stretchers,  straight  hard,  hard  and 
salmon''  and  hare  a  very  good  market  for  our  product.  We 
burn  the  brick  in  open  top  Dutch  kilns,  ten  arches  and  twelve 
inch  grates  through  the  kilns,  which  are  26  ft.  6  ins.  wide  and 
34  ft.  6  ins.  long.  We  set  the  bottom  work  sixteen  courses 
high  and  set  twenty  courses  on  top  of  this.  The  sides  of  the 
arches  are  set  ten  courses  high  straight,  with  six  hangers, 
that  have  a  one-inch  projection  to  form  the  arch.  We  get  a 
•very  good  grade  of  brick  in  the  twenty  top  courses,  and  in 
the  straight  part  below  the  arches,  as  well  as  in  the  middle, 
between  the  arches,  but  all  of  the  brick  in  the  facings  of  the 
arches,  from  the  tenth  to  the  sixteenth  course,  are  "dead" 


CLAYWORKING    PROBLEMS 


li       '  C 

nnnn 

i           n 
li          U 

1           1 

1 

DLMJOJ 
innni     i 

i    Rf 

n    ii~~tr~"ir 

<s-4z±-t- 

Dnnnr 

XG      II 

3C 

ii     i 

lUtiU 


A — Firing  Arch;  B — Kiln  Floor;  C — Nine  Courses  Hacked  as 
Shown  in  Fig.  2,  One-half  Inch  Apart;  D — the  Tenth  Course, 
Hacked  Tight;  T — One  Inch  Projection;  F — Five  Courses, 
Hacked  as  In  Fig.  2,  One-half  Inch  Apart;  G — Top  Hanger 
Brick  Hacked  as  in  Fig.  3,  Every  Other  One  Drawn  Back 
Two  Inches;  H — Six  Courses  on  Both  Sides  of  Arch  That 
Produce  "Dead"  Brick;  On  Top  of  G  Course,  the  Brick  Are 
Set  Five-on-two;  Then  Six  More  Courses,  Set  Six-on-two. 


58  CLAYWQRKING    PROBLEMS 

and  have  no  ring;  still  they  are  seemingly  sound  and  un- 
cracked.  We  often  get  a  number  of  cracked  brick  but  these 
are,  as  a  rule,  above  the  arches.  Our  clay  is  easy  to  burn, 
apparently,  as  the  tops  are  always  good,  and  we  cannot  tell 
whether  our  trouble  is  in  the  setting,  the  watersmoking,  the 
burning  or  the  cooling.  We  are  sending  you  a  sketch  show- 
ing the  setting,  and  will  appreciate  any  information  you  can 
give  us  in  this  matter.  Our  kilns  are  cooled  in  about  five 
days  and  four  nights,  and  burned  in  four  days  and  four 
nights.  The  brick  are  dried  in  a  pipe-rack  steam  dryer  and 
are  soft-mud  brick.  We  often  find  that  the  brick  that  are 
broken  have  a  glossy,  bright  face  on  the  fracture,  but,  when 
broken  again,  have  a  rough  texture.  I  would  like  to  know 
if  you  think  that  four  hangers,  with  a  one-and-one-half-inch 
projection  would  be  better  than  si.\'  hangers  with  a  one-inch 
projection,  and  would  also  appreciate  any  information  you 
can  give  me  as  to  the  best  method  of  setting  in  this  type  of 
kiln.  I  ivould  also  like  to  know  your  idea  of  the  best  method 
of  burning,  and  your  opinion  on  a  dead  middle,  instead  of  a 
grate  straight  through.  Give  me,  if  you  can,  the  size  of  the 
dead  middle  that  a  kiln  of  the  ividth  given  should  have,  and 
whether  there  should  be  any  fire  on  the  dead  middle  after 
the  ivatcrsmoking  period. 

The  setting  appears  to  be  all  right,  and  is,  in  fact,  the 
method  generally  employed  in  soft-mud  plants.  If  the  brick 
come  out  "shaky"  in  the  arch,  as  noted  in  the  question,  then 
our  opinion  is  that  the  one-inch  projection  is  better  than  four 
hangers  with  one-and-one-half  inch  projections.  With  the 
present  method  of  setting  the  arches,  a  higher  percentage  of 
the  brick  is  protected.  The  setting  of  four  brick,  with  the 
inch-and-a-half  projection  is,  however,  worth  trying,  since 
the  four  hangers  will  present  a  smaller  number  of  brick  in 
the  arches,  and,  perhaps,  less  loss. 

While  it  is  merely  theorizing,  we  cannot  see  why  the  water- 
smoking  or  the  burning,  or  the  cooling  should  cause  the 
trouble.  Why  it  singles  out  the  arch  brick,  disregarding  the 
risers  in  the  arch,  and  limiting  its  action  to  this  one  point, 


CLAYWOKKING    PROBLEMS  59 

is,  to  say  the  least,  curious.  The  courses  immediately  above 
the  arch — fourteen  high — are  set  five-on-two ;  certainly  this 
can  cause  no  back  pressure,  or,  in  other  words,  it  provides 
sufficient  space  to  carry  off  any  surplus  steam,  and,  later  on, 
high  heat.  The  arch  brick  themselves— set  six  high — are 
spaced  exactly  like  those  immediately  under  the  arch,  giving 
a  certain  draft  clearance — the  same  as  those  in  the  supporting 
wall.  Yet  these  latter  brick  absorb  and  give  out  heat,  or,  in 
other  words,  partake  of  all  fluctuations  in  temperature  that 
affect  the  arch  brick. 

It  is  possible  that  the  brick  which  immediately  adjoin  the 
arch  brick  and  back  them  up,  are  set  too  tightly — and  so  do 
not  allow  the  free  circulation  of  steam,  heat  and,  finally,  cold 
air  through  the  inter-spaces. 

Regarding  the  best  methods  for  burning — this  would  de- 
pend so  much  upon  the  character  of  the  clay,  that  a  discussion 
of  that  point  would  have  to  be  held  upon  the  yard,  rather 
than  several  hundred  miles  away.  The  location  and  size  of 
the  grates  also  depends  upon  actual  conditions  of  fuel,  mate- 
rial and  product,  and  would  also  have  to  be  determined  by 
experiment  made  under  practical  working  conditions. 


CLAYWORKING    PROBLEMS  61 


CHAPTER  II 

WHICH   DEALS  WITH  GLAZING 

Glazing  Sewer  Pipe 

40.  Indiana — What  is  considered  the  best  method  of  "salt- 
ing" a  kiln  of  seuvr  pipe?  Is  more  than  one  dose  needed? 

The  working  of  a  kiln  during  the  salting  period  varies 
according  to  the  class  of  material  used  and  the  color  re- 
quired of  the  finished  goods;  besides,  most  burners  have 
some  particular  fad  of  their  own  in  finishing  kilns,  i.e., 
whether  the  goods  are  finally  burned  in  an  oxidizing  or  a 
reducing  atmosphere. 

It  is  well  understood  that  the  glazes  produced  by  the 
use  of  salt  have  no  coloring  power  in  themselves,  and  by 
proper  working  the  glaze  is  transparent.  If,  however,  the 
kiln  contains  a  quantity  of  carbon  (which  is  a  strong  re- 
ducing agent),  in  the  form  of  smoke,  when  the  salting  is 
carried  out  the  glaze  will  be  rendered  much  darker  in 
color  (to  brown  and  very  deep  brown). 

(The  carbon  only  acts  indirectly  by  reducing  the  iron 
compounds  in  the  clay. — Editor.) 

A  capable  burner  should  be  able  to  keep  his  kiln  under 
control,  and  produce  whatever  colors  are  desired.  To 
prepare  for  salting,  it  is  first  necessary  to  note  that  the 
Seger  cone  used  (generally  7  or  8)  indicates  that  the  re- 
quisite temperature  has  been  reached,  or  where  no  cones 
are  used,  that  the  trials  are  satisfactory.  The  fires  imme- 
diately before  salting  must  be  clear,  bright,  and  shining 
through  the  bars;  the  interior  of  the  kiln  must  be  free 


62  CLAYWORKING    PROBLEMS 


from  smoke.  The  damper  should  be  lowered  to  within 
three  inches  of  the  bottom. 

It  is  then  necessary  to  go  the  round  of  the  fires  as 
quickly  as  possible,  putting  a  good  shovelful  of  salt  well 
into  the  back  of  each  firehole. 

Immediately  after  salting,  the  mouth  of  each  firehole 
should  be  covered  with  an  iron  plate  kept  for  that  pur- 
pose. After  fifteen  minutes  or  so  raise  the  damper  and 
fire  to  regain  the  loss  of  temperature.  The  temperature 
of  the  kiln  must  be  raised  to  what  it  was  before  salting, 
as  the  addition  of  the  salt  has  lowered  it  about  250  de- 
grees C.  When  the  original  temperature  has  again  been 
reached  the  damper  is  lowered  once  more,  and  another 
salting  similar  to  the  first  carried  out.  After  fifteen  to 
twenty  minutes  the  damper  is  again  raised,  and  the  kiln 
heated  up  as  before. 

When  the  kiln  clears,  a  trial  piece  should  be  drawn  and 
examined.  If  it  shows  a  good  glaze,  allow  the  fires  to 
burn  clear,  and  apply  a  final  salting  with  a  stronger 
draught  on  the  kiln  than  in  the  previous  saltings,  so  as 
to  brighten  up  the  glaze.  Trial  pieces  should  again  be 
drawn,  and  if  satisfactory  no  further  salting  is  neces- 
sary. After  the  last  salting  four  or  five  firings  at  high 
heat  are  necessary  to  form  and  fix  the  glaze,  but  ex- 
cessively long  and  continuous  firing  after  the  last  salting  is 
simply  a  waste  of  fuel.  During  these  final  firings  the 
damper  is  kept  open.  The  last  fire  should  be  allowed  to 
burn  itself  down,  so  as  not  to  provide  a  reducing  at- 
mosphere inside  the  kiln  after  closing. 

The  kiln  should  be  cooked  fairly  quickly,  especially  at 
first,  as  slow  cooling  tends  to  dull  the  glaze.  After  the 
goods  reach  a  dark  red,  heat  cooling  must  be  much  slower 
to  prevent  cracking.  To  effect  this,  all  the  openings  are 
now  blocked  up  and  daubed  over  to  make  the  kiln  air- 
tight. The  kiln  is  then  allowed  to  cool  slowly,  the  heat 


CLAYWORKING    PROBLEMS  6a 

being  gently  drawn  away  by  leaving  the  damper  open  a 
little. 

In  about  four  days  the  kiln  will  be  ready  for  emptying. 


Salt  Glazing  Hollow  Building  Block 

381.  Texas — How  many  tons  of  salt  arc  necessary  in  glaz- 
ing hollow  building  tile  made  front  a  fire  clay?  (2)  We  use 
a  round  douit-draft  kiln  containing  100  tons  of  hollon1  build- 
ing tile.  At  it'hat  temperature  should  the  tile  be  burned  be- 
fore the  salt  is  applied?  (3)  How  long  should  the  heat  be 
kept  up  before  closing  the  kiln?  (4)  What  should  be  done 
u-ith  the  drafts  on  the  kiln  at  the  time  of  salting?  (5)  Hou' 
li'ide  apart  should  the  tile  be  set  to  insure  at  least  a  95%  and 
if  Possible  100%  salt  glased  uvrc? 

Some  clays  require  salting  more  times  than  others  and  for 
this  reason  no  figure  as  to  the  amount  required  will  suit  all 
cases.  However,  about  150  Ibs.  of  salt  per  100  tons  of  ware 
probably  represents  an  average  figure.  (2)  The  ware  in 
question  should  always  be  at  a  practically  maturing  tempera- 
ture before  an  attempt  is  made  to  salt.  (3)  The  fire  should 
not  be  kept  up  much  longer  after  salting— three  or  four  hours 
and  not  longer  than  six  hours.  (4)  The  manipulation  of  the 
draft  depends  upon  the  amount  you  are  carrying.  Generally 
speaking  it  should  be  cut  when  salting.  It  must  not  be 
thought,  however,  that  the  draft  should  be  completely  shut 
off.  for  if  this  were  done  it  is  apparent  that  the  salt  vapors 
would  not  he  drawn  down  through  the  ware.  On  the  other 
band  if  the  draft  be  too  strong  the  salt  fumes  will  be  drawn 
out  through  the  stack  so  quickly  that  they  do  not  have 
time  to  act  on  the  ware.  (5)  It  is  an  impossibility  to  state 
just  how  far  apart  the  ware  should  be  set  to  obtain  95  to 
100%  good  salt  glazed  ware.  The  essential  thing  is  to  see 
that  adjacent  tile  do  not  touch,  thereby  preventing  the  salt 
fumes  from  entering  between  them.  It  is  also  necessary  that 


CLAYWORKING    PROBLEMS 


all  the  slits  in  the  kiln  floor  be  well  open,  for  if  otherwise 
ihe  ware  above  it  would  be  apt  to  be  poorly  glazed  or  not 
at  all. 


Salt  Glaze  for  Drain  Tile 

:.)(.)4.  Michigan — Please  let  me  know  the  best  way  to  pul 
ti  salt  alaze  on  drain  tile.  U'e  hare  been  working  on  drain 
tile  and  wish  to  qlaze  same.  Our  company  is  a  new  one,  hctr- 
infj  started  only  last  August. 

Salt  glazing  drain  tile  is  practically  the  same  proposition 
as  applying  this  type  of  glaze  to  any  other  ware,  such  as 
conduits  or  sewer  pipe.  In  any  case  the  temperature  must 
be  high  and  the  body  practically  mature.  The  following  para- 
graphs are  extracted  from  Searle's  book,  "Modern  Brick 
Making."  Considerable  space  is  given  to  the  subject  of  salt 
glazing  and  necessarily  only  a  portion  of  the  same  can  be 
used  here : 

"In  simple  glazing  with  salt,  the  glaze  is  really  formed 
from  part  of  the  salt  combining  with  part  of  the  clay,  so 
that  the  glaze  is  necessarily  far  more  adhesive  than  when  all 
the  constituents  of  the  glaze  are  mixed  together  and  applied 
in  the  form  of  a  slip  or  spray. 

"All  clays  are  not  suitable  for  glazing  with  salt,  as  it  is 
found  that  a  certain  temperature  (corresponding  to  cone  2 
but  more  usually  cone  7)  is  essential  for  the  full  development 
of  the  glaze,  and  that  the  proportion  of  alumina  and  silica 
must  be  within  comparatively  narrow  limits.  L.  E.  Barringer 
has  shown  that  the  most  suitable  clays  are  those  containing 
about  0:5  per  cent  silica  and  23  per  cent  alumina,  but  provided 
there  is  not  less  than  3  Ibs.  or  more  than  8  Ibs.  of  silica  to 
each  pound  of  alumina  in  the  clay  a  good  glaze  may  be  ob- 
tained. Some  clays  outside  these  limits  can  be  salt-glazed, 
but  will  not  give  really  good  results.  The  state  in  which  the 
silica  is  present  does  not  appear  to  be  important,  and  some 
clays  which,  alone,  cannot  be  salt-glazed,  will  give  excellent 


CLAYWORKING    PROBLEMS  65 

results  when  mixed  with  very  fine  sand,  but  coarse  or  medium 
sand  cannot  be  used  for  this  purpose.  The  best  results  are 
obtained  with  clays  which  begin  to  vitrify  at  the  temperature 
at  which  the  salt  is  added,  but  which  do  not  lose  their  shape 
until  a  far  higher  temperature  is  reached. 

"The  kilns  used  in  salt-glazing  may  be  single  or  continuous 
(chamber)  kilns,  though  there  are  disadvantages  in  the  latter 
unless  they  are  used  exclusively  for  salt  glazing.  In  most 
work  it  is,  therefore,  better  to  use  separate  down-draft  kilns 
with  a  perforated  or  false  bottom.  There  must  be  ample 
grate  area  in  the  fire-boxes,  and  the  generally  accepted  rule 
amongst  the  builders  of  salt-glazed  kilns — viz.,  6  sq.  ft.  kiln 
area  for  each  fire-box — is  generally  satisfactory.  As  the 
damper  in  the  main  flue  of  the  kiln  is  of  great  importance 
in  salt-glazing,  care  should  be  taken  that  it  fits  well  and  is 
kept  in  good  order.  The  brickwork  must  be  tight,  as  a 
good,  sharp  draught  is  needed  during  some  parts  of  the  fir- 
ing. The  goods  are  placed  so  that  there  is  ample  room  for 
the  salt  to  reach  the  faces  to  be  glazed,  but  apart  from 
this  they  are  set  just  as  if  they  were  ordinary  glazed  brick. 
To  some  extent  the  method  of  setting  depends  upon  the 
number  of  headers  and  stretchers  required  to  be  set." 


Recipes  for  Enameling  Black,  Blue  and  Green 

399.  Pennsylvania — Prof.  R.  T.  Stull  gives  us  some  very 
valuable  information  on  "How  to  Enamel  Brick,"  in  his 
article  printed  in  "Brick  and  Clay  Record,"  but  he  does  not 
say  where  the  recipes  could  be  secured  to  enamel  black,  blue 
and  green. 

We  asked  Professor  Stull  to  supply  us  with  the  desired  in- 
formation. Here  is  his  answer  in  full : 

"There  are  two  methods  of  producing  an  enamel  surface  on 
brick,  one  is  by  applying  an  engobe  or  slip  to  the  face  of  the 
brick  then  applying  a  clear  glaze  over.  The  other  method 


66  CLAYWORKING    PROBLEMS 

is  to  apply  an  oqaque  glaze  or  enamel  to  the  face  of  the  brick 
without  using  an  engobe  or  slip. 

"The  method  of  procedure  for  making  colored  enamel 
brick  depends  upon  whether  the  slip  and  glaze  method 
is  used  or  whether  the  enamel  proper  is  used.  The  colors 
are  produced  by  the  use  of  either  raw  oxides  or  prepared 
stains. 

"If  a  coloring  material  is  added  to  a  clear  glaze  and  goes 
into  solution  during  fusion  of  the  glaze  it  will  give  an  un- 
even color  because  the  color  will  be  dark  where  the  glaze 
is  thick  and  light  where  the  glaze  is  thin.  In  order  to  ob- 
tain a  uniform  color  where  the  slip  and  clear  glaze  method  is 
used  for  making  enamel  brick,  the  coloring  agent  is  added  to 
the  slip  or  engobe  where  it  is  practical  to  do  so.  Sometimes 
part  of  the  color  is  added  to  the  slip  and  part  to  the  glaze. 

"Where  the  slip  is  dispensed  with  and  the  opaque  glaze 
or  enamel  is  applied  directly  to  the  face  of  the  brick,  the 
color,  when  added  to  the  enamel,  will  be  uniform  whether  the 
enamel  be  thin  or  thick. 

"Some  of  the  recipes  of  stains  which  may  be  added  to  an 
otherwise  colorless  glaze  enamel  or  engobe  for  producing 
blues,  greens  and  blacks  are : 


BLL 

JES 

No.    1 

No.  2 

English  china  clav.  .  . 

IS 

Aluminum  oxide    

205 

Cobalt   oxide    .  .  .  .'  

...  .    12 

Cobalt   oxide    

Zinc   oxide    

....      6 

Magnesium  carbonate  .  . 

'.  '.  .  .16S 

Potters   flint    .  .  . 

IS 

Saltpeter    

....      6 

No.   3 

No.  4 

Coball  oxide   .... 
Potters   flint    '.' 
Carbonate  of  potash 

...  .250 
....165 

Aluminum   oxide    
Cobalt  oxide    

.  ...   40 

Saltpeter     .,'.] 

42 

No.  5 

No    6 

Aluminum  oxide  .  .  . 
Zinc  oxide  

30 
....      6 

Cobalt  phosphate  
Aluminum   oxide 

...183 
.  .103 

Cobalt  carbonate  

....      4 

No.  7 

No    8 

Zinc    oxide    
Cobalt  phosphate  

213 
345 

Cobalt  oxide    .  .'  
Chronic  oxide 

,...166 
76 

Aluminum  oxide    .  .  . 

515 

Aluminum   oxide    

,...155 

CLAYWORKING    PROBLEMS 


67 


GRE 

ENS 

No.  9 

No.  10 

Nickel  oxide    

,,..150 

Bichromate    of    potash 

..   36 

Chrome  oxide   

76 

Fused    calcium    chloride.. 

..   12 

Potters   flint    

,  .   20 

Potters  whiting   

..   20 

| 

Fluorspar    

..   12 

No.  11 

No.  12 

Barium  chromate   

..   46 

Chrome  oxide   

..120 

Potters  whiting  

...   34 

Potters  flint  

..395 

Boracic  acid    

20 

Potters  whiting  

..     5 

No.  13 

No.  14 

Chrome  oxide   

128 

English  china  clay  

255 

Cobalt  oxide  

..     1 

Chrome    oxide    , 

150 

Potters  flint    

..   43 

Potters  whiting  , 

35 

Borax   

..     4 

BLA 

CKS 

No.  15 

No.  16 

Red  oxide  of  Iron  

40 

Red  oxide  of  Iron  

,,    80 

Chrome  oxide   

....   76 

Chrome  oxide   

..   76 

Cobalt  oxide    

.,   20 

No.  17 

No.  18 

Chromate  of  Iron  

....445 

Chrome    oxide    

137 

Cobalt  oxide    

55 

Red  oxide  of  iron  

192 

Oxide  of  manganese  

..140 

Cobalt  oxide   

..   50 

No.  19 

Red  oxide  of  iron  

...172 

Chrome  oxide  

172 

Oxide  of  manganese  

40 

Cobalt  oxide   

,  .  .  ,    16 

"The  colors  should  be  weighed  from  the  dry  powder  mate- 
rials and  thoroughly  mixed  by  grinding.  These  should  be 
calcined  strongly  and  ground  wet  in  a  ball  mill  fine  enough  to 
pass  a  150  mesh  screen.  The  ground  colors  should  next  be 
washed  four  or  five  times  by  decantation  and  dried  ready  for 
use. 

"In  order  to  produce  the  shade  of  color  desired  add  from 
1%  to  10%  of  the  color  stain  to  the  glaze  or  enamel  or  from 
2%  to  15%  to  engobes. 

"The  addition  of  the  stain  to  the  glaze  or  enamel  frequent- 
ly throws  the  glaze  or  enamel  out  of  balance.  Some  stains 
render  the  glaze  or  enamel  less  fusible  while  others  lower 
the  fusion.  Usually  stains  are  basic  in  character  and  in  order 
to  get  a  balance  colored  glaze  it  is  necessary  to  reduce  the 
base  in  the  glaze,  such  as  lowering  the  whiting  or  zinc  or 


CLAYWORKING    PROBLEMS 


lead  or  alumina  or  similar  results  may  be  had  raising  the 
silica  (flint)  of  the  glaze. 

"In  producing  green  colors  by  the  use  of  chrome  oxide  or 
stains  containing  it,  the  original  glaze  or  enamel  to  which 
the  coloring  material  is  added  should  not  contain  zinc  oxide. 
If  zinc  oxide  is  present  it  tends  to  destroy  the  green  color 
and  produce  an  uneven  dirty  brown. 

"On  the  other  hand,  zinc  oxide  intensifies  the  blue  color 
of  cobalt  oxide  and  is  therefore  a  valuable  component  in  the 
production  of  cobalt  blues. 

"Black  is  one  of  the  most  difficult  to  produce  of  all  the 
colors  in  the  ceramic  category.  Very  few  ceramic  colors 
can  be  classed  as  jet  black.  They  are  as  a  rule  either  blue- 
black,  green-black  or  brown-black  when  placed  on  a  white 
body.  Blacks  should  be  placed  over  a  colored  body  either 
a  buff  or  a  red." 


Wants  to   Know  About  Salt-Glazing 

621.  Kentucky — We  have  just  had  our  clay  tested  for  salt- 
glazing  and  find  that  it  will  take  the  glaze  by  only  a  very 
narrow  margin,  and  we  would  like  to  have  about  all  of  the 
information  you  can  give  us  as  to  the  mode  of  procedure  in 
salt-glazing,  as  we  are  going  to  make  silo-block  and  want  to 
glaze  them.  We  want  to  know  more  than  we  know  now, 
about  handling  the  dampers  and  applying  the  salt.  We  have 
a  twenty-six-foot  round,  down-draft  kiln,  with  slanting  grate- 
bars,  ten  fire-holes  or  furnaces,  bag-walls  about  seven  feet 
high — nine  wall  stacks  and  kiln  floor  perforated  with  a  twelve- 
foot  circle  in  center,  and  one  large  circle  flue  outside  of  this. 
We  get  very  good  burns  on  our  drain  tile,  down  to  the  very 
floor. 

The  fact  that  you  have  a  kiln  which  burns  good  drain  tile 
to  the  very  bottom  settles  the  question  of  your  having  the 
right  equipment.  As  to  the  clay — that  is  another  matter.  In 
the  first  place,  we  would  suggest  your  reading  the  paper  that 


CLAYWORKING    PROBLEMS 


was  read  by  L.  E.  Barringer,  E.  M.,  before  the  American 
Ceramic  Society,  in  1902.  This  was  published  in  Vol.  IV  of 
the  Transactions  of  the  American  Ceramic  Society,  and  may 
be  obtained  from  the  secretary,  Edward  Orton,  Jr.,  Colum- 
bus, Ohio,  for  $4.75,  bound  in  cloth,  or  $4.00,  bound  in  paper. 
The  title  of  Mr.  Bar  ringer's  address  was  "The  Relation  be- 
tween the  Constitution  of  a  Clay,  and  Its  Ability  to  Take  a 
Good  Salt  Glaze."  In  "Brick  and  Clay  Record,"  issue  of 
Sept.  15,  1914,  on  page  616,  a  short  article  appears,  which 
may  be  of  some  assistance.  In  order  to  save  your  going 
through  your  old  files,  we  will  publish  it  again : 

Bring  the  kiln  up  to  a  pre-finish  heat.  Quickly  get  the  fur- 
naces white  hot  with  a  very  thin,  clean  fire.  Sprinkle  one 
shovelful  of  salt  evenly  over  this  prepared  bed  of  coal.  Drop 
damper  as  low  as  possible,  allowing  a  very  stagnant  draft. 

When  the  salt  fumes  become  thin,  open  the  damper  and 
regain  lost  heat  in  the  fire  boxes.  Repeat  the  operation. 

A  finish  is  indicated  by  drawing  trials. 

It  is  best  to  start  the  glazing  operation  before  the  total 
settle  is  obtained,  as  the  operations  noted  above  will  keep 
the  kiln  settling,  although  the  body  heat  of  the  kiln  is  re- 
duced. 


Wants  Salt  for   Glazing 

672.  Georgia — We  would  like  to  have  the  address  of  par- 
ties at  the  nearest  points  to  us  from  whom  we  can  obtain  rock 
salt  or  any  other  salt  for  glasing,  and  will  greatly  appreciate 
it  if  you  can  give  us  this  information. 

The  International  Salt  Company  of  Atlanta,  Georgia  car- 
ries salts  at  the  ports  and  probably  has  some  second  quality 
salt  which  is  suitable  for  the  purpose  of  glazing.  The  Myles 
Salt  Company,  Ltd.,  of  New  Orleans,  La.,  would  also  be  in 
a  position  to  make  prices,  as  well  as  the  Colonial  Salt  Com- 
pany of  Akron,  Ohio.  We  are  under  the  impression  that 
you  have  made  an  error  in  suggesting  "rock  salt"  as  we  do  not 


CLAYWORKING    PROBLEMS 


believe  that  you  will  have  any  success  in  using  this  particular 
kind  of  salt  for  the  purpose  of  glazing  sewer  pipe  or  other 
clay  products. 


Gets  Blue  Glaze  on  Stoneware 

657.  California — We  enclose  two  small  samples  of  stone- 
ware "try-pieces."  These  arc  both  fired  on  top  and  one  of 
them  was  drazvn  immediately  as  we  stopped  firing.  The  other 
zvas  drawn  after  the  kiln  had  cooled.  We  find  that  the  fin- 
ished ware  looks  like  the  blue  "try-piece."  The  kiln  is  down- 
draft,  with  a  stack  in  the  center;  we  have  fired  it  several  times 
and  have  found  in  each  instance  that  after  we  stopped  firing 
the  glaze  on  the  ware  turned  blue.  We  believe  that  this  is 
caused  in  the  cooling  of  the  kiln,  as  the  "try-piece"  that  was 
drawn  at  the  time  we  stopped  firing  is  perfectly  zvhite  while 
the  one  that  was  drazvn  after  the  kiln  had  cooled  has  the  dull 
blue  finish. 

In  cooling  we  closed  the  damper  in  the  stack  immediately 
after  firing  and  opened  all  of  the  holes  in  the  top  of  the  kiln; 
about  thirty  minutes  later  zve  closed  up  the  fire  boxes.  We 
have  also  tried  leaving  the  fire  boxes  open  for  three  hours  or 
until  they  had  turned  black  but  on  each  occasion  we  closed 
the  damper  in  the  stack  at  the  time  the  firing  stopped.  It 
might  be  well  to  call  your  attention  to  the  fact  that  our  firing 
is  done  with  crude  oil.  If  you  will  give  us  your  opinion  in 
regard  to  the  reason  why  this  zi'are  turns  blue  after  firing,  we 
would  appreciate  your  advice  and  assistance. 

Every  indication  points  to  a  peculiar  condition  in  this  kiln — 
it  is  that  it  contains  a  reducing  atmosphere  after  the  firing 
is  finished.  What  fault  in  construction  causes  this  condition 
is  impossible  to  even  suggest  without  personal  observation. 
The  "try-pieces"  toge'ther  with  the  explanation  given  in  the 
question  are  indications  of  the  condition  mentioned.  In  order 
to  cure  that  condition  further  experiments  will  have  to  be 


CLAYWORKING    PROBLEMS 


made  which  will  tend  to  make  a  complete  change  in  the  kiln 
atmosphere  when  the  firing  is  completed. 

It  may  be  that  the  glaze  absorbs  iron  from  the  surface  of 
the  body  or  that  the  glaze  contains  iron  in  ferric  state  and 
that  this  is  reduced  slightly  during  cooling.  The  question  and 
the  answer  herein  given,  together  with  the  "try-pieces"  have 
all  been  submitted  to  Professor  Stull  of  the  University  oi 
Illinois. 

The  above  question  was  published  in  the  June  1  issue. 
Professor  StulPs  reply  is  given  below : 

No  doubt  you  have  read  Robert  Burns'  ode  to  a  famous 
physician  who  could  prescribe  curatives  based  upon  evidence 
sent  to  him  in  a  "Kale"  leaf.  There  are  no  doctors  in  this 
day  and  age  of  enlightenment,  who  are  as  wise  as  the  famous 
doctor  of  Burns'.  With  the  exception  of  a  few  simple  cases, 
the  "ceramic  doctor"  cannot  prescribe  intelligently  from  a 
few  symptoms  sent  to  him  by  mail. 

The  physician  prefers  to  be  on  the  ground  and  examine 
the  patient  thoroughly  by  thumping  him  on  the  chest,  ex- 
amining his  tongue,  and  taking  his  temperature  and  his  pulse. 
From  the  symptoms  thus  gathered,  the  "Doc"  decides  whether 
the  patient  has  small-pox  or  the  "pip"  and  prescribes  accord- 
ingly. Sometimes  "Doc"  is  undecided  as  to  whether  the  ill- 
ness is  due  to  the  "pip"  or  the  small-pox  or  whether  it  is 
due  to  something  else.  At  any  rate  he  always  looks  wise 
and  in  the  latter  case  applies  a  "shotgun  prescription"  trust- 
ing that  it  will  get  at  the  seat  of  the  trouble. 

Thus  it  is  with  the  "clay  doctor."  Seldom  is  he  able  to 
prescribe  effectively  unless  he  is  right  on  the  ground  and 
carefully  studies  the  operations  from  the  clay  bank  through 
to  the  stock  pile.  Even  though  the  "clay  doctor"  may  be 
well  trained  in  his  line  and  backed  by  years  of  successful 
experience,  he  not  infrequently  finds  cases  that  are  baffling, 
even  in  the  present  light  of  our  ceramic  knowledge.  And  so 
the  "clay  doctor"  not  infrequently  applies  a  "shotgun  pre- 


CLAYWORKING    PROBLEMS 


scription''  taking  care  not  to  include  anything  that  will  work 
disastrously. 

By  examination  of  the  evidence  at  hand  in  California's 
case,  we  find  that  trial  piece  No.  1  drawn  from  the  kiln  at 
the  finish  shows  a  good  white  glaze  of  excellent  gloss  for  a 
stoneware  glaze.  Trial  No.  2  which  cooled  in  the  kiln  is 
dull  and  I  should  say  of  a  brownish  shade  rather  than  blue 


Trial   No.  1 


Trial   No.  2 


and  shows  spots  apparently  of  iron  fused  through  the  glaze. 
A  fracture  of  trial  No.  1  shows  that  the  body  is  a  good 
light  stoneware  gray  color,  while  a  fracture  of  No.  2  reveals 
a  darker  blue  stone  appearance  with  occasional  spots  of  gray 
buff.  No.  1  shows  a  few  black  specks  while  No.  2  shows 
a  large  number  of  them.  Close  inspection  of  No.  2  shows 
that  there  is  a  thin  dark  brown  layer  or  skin  under  the  glaze 
which  has  fused  through  in  spots  and  along  the  edges.  The 
appearance  of  the  trials  would  indicate  that  the  black  specks 
are  due  to  iron— probably  present  in  the  clay  in  the  form  of 


CLAYWORKING    PROBLEMS 


pyrite.  The  clay  has  evidently  been  screened  about  60  to 
80  mesh. 

Trial  No.  1  being  a  good  clean  light  stoneware  gray  would 
indicate  that  the  firing  has  been  done  oxidizing  up  to  the 
finish.  The  blue  stone  appearance  of  trial  No.  2  and  its 
dark  brown  skin  underneath  the  glaze  and  dark  brown 
blotches  fused  through  resemble  the  same  effect  as  is  pro- 
duced by  "flashing."  As  is  well  known,  flashing  is  produced 
by  alternate  oxidation  and  reduction.  The  same  effect  may 
be  caused  by  steam  or  water  vapor  in  contact  with  the  ware 
within  the  kiln  chamber,  at  or  below  the  finishing  tempera- 
ture. The  dull  or  dead  appearance  of  the  glaze  may  be 
caused  by  cooling  in  a  "sulphurous"  atmosphere  or  in  an  at- 
mosphere of  superheated  water  vapor.  It  is  possible  that 
a  reducing,  a  "sulphurous"  or  a  vapor  laden  atmosphere  may 
exist  for  a  short  time  after  the  damper  is  closed  and  the 
kiln  finished.  The  oil  used  as  fuel  very  likely  contains  sul- 
phur, although  not  stated,  and  it  is  probably  vaporized  by 
steam.  If  oil  and  steam  should  escape  into  the  fire-boxes 
through  leaky  valves  and  connections  after  the  damper  has 
been  closed,  a  very  bad  atmosphere  in  the  kiln  chamber  may 
exist  for  a  short  time. 

As  a  rule,  glazes  have  a  better  gloss  when  cooled  rapidly. 
There  is  very  little  danger  of  cracking  by  rapid  cooling  for 
a  short  time  after  the  kiln  is  finished.  The  greatest  danger 
in  cracking  lies  in  too  rapid  cooling  from  red  heat  (about 
1,100  degrees  Fahr.)  down  to  atmospheric  temperature. 

For  the  "shotgun  prescription"  the  following  recommenda- 
tions are  made.  It  might  not  be  advisable  to  try  all  these  at 
once,  but  on  the  contrary  it  would  be  more  logical  to  try 
one  at  a  time  and  observe  the  results. 

Use  water  free  from  sulphates  in  washing  and  tempering 
the  clay.  Screen  the  clay  finer.  Do  not  use  the  water  from 
the  filter  press  over  again.  In  pugging  the  washed  clay,  add 
a  little  barium  carbonate,  taking  care  that  it  is  uniformly 
distributed  and  pugged  in,— about  6  to  18  Ibs.  per  ton  of 
dry  clay  should  be  sufficient.  Set  the  ware  in  the  kiln  in  the 


CLAYWORKING    PROBLEMS 


bone-dry  condition.  Fire  the  kilns  with  a  good  clean  oxidiz- 
ing atmosphere.  After  the  burners  are  shut  off  at  the  finish, 
see  that  no  oil  or  steam  is  leaking  in  the  fire-boxes.  After 
the  finish,  when  the  burners  are  shut  off,  leave  the  fire-boxes 
open,  the  damper  partly  open  and  the  crown  ventilators  closed, 
allowing  the  kiln  to  cool  rapidly  for  a  short  time.  The  length 
of  time  of  this  rapid  cooling  without  damage  to  the  ware 
should  be  determined  by  experiment.  After  the  safe  limit 
of  rapid  cooling  has  been  reached,  close  the  damper  and  open 
some  of  the  crown  ventilators  a  little.  If  the  kiln  is  tight 
(i.  e.,  not  leaky)  the  remainder  of  the  cooling  can  be  gov- 
erned by  the  crown  ventilators  without  closing  the  fire-boxes 
unless  the  clay  is  very  sensitive  to  cracking. 


Salt  Glazing  in  Oil  Fired  Kilns 

679.  New  Jersey — -Can  you  gk'c  us  any  information  on  the 
use  of  salt  for  glazing  clayware  burned  in  oil-fired  kilns? 
Should  the  salt  be  fed  in  with  the  blast  from  the  burner  or 
introduced  into  the  furnace  through  a  separate  opening,  so 
that  the  flame  may  play  upon  it  on  the  furnace  bed? 

The  above  question  was  published  in  the  June  15  issue  and 
an  answer  given  which  was  admittedly  theoretical.  Since 
that  time  a  letter  has  been  received  from  E.  J.  Jones,  of  Can- 
ton, Ohio,  who  cites  an  experience  with  natural  gas  as  a 


Looking    Down    into    the    Fire    Box 


CLAYWORKING    PROBLEMS 


fuel.  As  his  plan  should  work  equally  well  with  oil  under 
pressure,  it  is  given  in  detail.  His  letter  reads  as  follows: 

"I  am  enclosing  sketches  of  the  fire  boxes  that  I  used  and 
with  which  I  had  successful  results  firing  with  natural  gas 
on  the  salt  glazed  face-brick. 

"Two  brick  on  edge  (B  in  sketch)  were  placed  about  op- 


A  -  Brick    Laid    Loose    to   Fill    Bottom 
S  -  4  Bricks   on  Edge  to   Break  up   Soli- 
C  -  Loose    Br!ck-use  more  to    Regulate  Air 
D  •  Holes   to  open  or  close  for  Regulation  of  Air 
A    Cross-Section    View   of   the    Furnace 

posite  the  spaces  on  either  side  of  the  center  burner.  Brick 
(C)  are  laid  loose  on  hob  of  kiln  in  front  of  the  firing  arch 
and  in  some  cases  and  stages  of  firing  it  may  be  found  neces- 
sary to  lay  one  or  two  courses  more  to  regulate  air-intake 
which  depends  entirely  upon  the  draft  construction  of  the 
kiln.  The  table  is  to  cover  the  entire  surface  inside  of  the 
fire-box.  I  might  add  that  in  throwing  in  the  salt  a  burner 


CLAYWORKING    PROBLEMS 


should  grasp  the  handle  of  the  shovel  and  give  the  shovel  a 
twisting  movement  so  as  to  scatter  the  salt  over  as  wide  an 
area  as  possible — that  is,  covering  as  large  a  space  on  the 
table  as  he  can  rather  than  throwing  the  salt  in  one  pile. 

"I  have  also  noted  that  the  shorter  the  salting  period  the 
more  brilliant  the  glaze  and  the  less  iron  drawn — for  instance, 
using  five  barrels  of  salt  in  three  hours  gave  a  much  brighter 


Front  View  of  the   Fire    Box 

glaze  than  using  the  same  quantity  in  six  hours,  all  other 
conditions  being  the  same. 

"I  found  it  better  to  use  a  long  yellow  flame  instead  of  a 
short  blue  flame  in  salting  and  to  use  one  shovel  of  salt  each 
round,  making  three  rounds  about  ten  minutes  apart  for  each 
salting  period. 

"You  will  note  by  the  sketches  that  the  opening  was  left 
under  the  old  coal-fire  arch  just  large  enough  to  admit  a 
No.  2  dirt  shovel. 

"By  adopting  the  above  process  I  was  able  to  produce  sev- 


CLAYWORKING    PROBLEMS  77 

eral  kilns  of  brick  with  full  bright  glaze  and  color  where 
before  this  method  was  used  we  could  get  hardly  more  than 
the  top  third  of  the  kiln  to  take  a  full  glaze." 

John  A.  Miller,  president  of  the  Rochester  Clay  Products 
Company,  Rochester,  Pa.,  writes: 

"If  your  New  Jersey  correspondent  (Question  No.  679  in 
June  15  issue)  will  write  the  Monmouth  Pottery  Company  at 
Monmouth,  111.,  they  may  give  him  the  information  he  asks 
for.  They  made  salt  glazed  stoneware  at  that  plant  several 
years  ago  and  used  oil  for  fuel  with  steam  pressure.  The 
writer  started  them  in  making  a  white  opaque  glaze  and  they 
discontinued  making  salt  glazes." 


Cannot  Glaze  Entire  Kiln 

688.  Iowa — Can  you  give  us  the  name  of  a  company  which 
manufactures  a  glazing  material  that  will  glaze  at  a  tempera- 
ture under  2,000  deg.  Fahr.f  We  can  glaze  three  or  four 
courses  in  the  top  of  our  kilns  with  salt  but  we  cannot  get 
high  enough  temperature  to  glaze  the  rest  of  the  kiln  without 
overturning.  We  are  making  glazed  silo  blocks  and  can  glaze 
only  one-third  of  the  kiln  at  a  burning. 

We  believe  that  your  trouble  does  not  lie  in  the  glazing 
material  that  you  have  been  using  (which  we  presume  is  com- 
mon salt)  but  in  your  method  of  applying  it. 

Perhaps  we  could  make  this  plainer  by  saying  that  we  do 
not  believe  you  are  burning  your  kilns  correctly  if,  in  order 
to  glaze  from  top  to  bottom  you  are  so  certain  to  overburn 
them.  The  fact  that  you  can  glaze  three  or  four  courses  in  the 
top  of  the  kiln  is  proof  that  your  ware  will  take  the  glaze 
high  as  to  endanger  the  ware.  The  trouble  seems  to  be  that 
you  cannot  get  as  high  a  temperature  at  the  bottom  of  the 
kiln  as  you  get  at  the  top,  and  this  is  due  to  some  fault  in 
your  burning  system.  Either  your  dampers  do  not  work 


78  CLAYWORKING    PROBLEMS 


properly  or  you  crowd  your  kiln  so  that  the  heat  does  not  get 
a  chance  to  bank  up  in  the  bottom  of  the  kiln  but  races 
through  and  out  of  the  stack. 

A  great  deal  has  been  published  on  the  subject  of  salt- 
glazing  in  this  department  and  we  are  under  the  impression 
that  if  you  will  follow  the  advice  that  has  been  given  other 
readers,  you  will  have  results  equally  as  good  as  those  which 
they  have  obtained.  It  may  be  that  you  have  not  seen  these 
articles  and  if  so,  we  will  be  glad  to  have  you  write  us  again 
on  the  subject  and  to  see  what  can  be  done  in  the  way  of 
sending  copies  to  you. 

It  looks  to  us  as  though  you  might  be  a  pretty  good  "pros- 
pect" for  some  manufacturer  of  pyrometers. 


CLAYWORKING    PROBLEMS 


7 '.I 


CHAPTER  III 


WHICH   DEALS   WITH    DIES 


End  Cut  Stiff  Mud  Brick  Shows  Die  Lamination 
88.  Tennessee — We  are  having  trouble  with  die  lamination. 
Ours  is  a  very  short  clay,  and,  after  it  is  loaded  on  cars  with 
drag-scrapers,  it  is  pugged  in  a  twelve  foot  pug-mill,  with 
two  rows  of  knives  on  a  central  shaft,  then  it  goes  to  a 
Chambers  end-cut  machine,  using  a  one-and-five-cighths  turn 
auger,  then  through  a  Chambers  lubricated  die,  which  is 
lubricated  with  a  cheap  black  lubricating  oil. 

The  following  article,  republished  from  "Brick  and  Clay 
Record"  of  December  15,  1912,  will  answer  your  question. 
It  is  by  Ray  Thos.  Stull,  E.  M.  (in  Cer.)  assistant  professor 
of  Ceramics,  University  of  Illinois. 

In  the  manufacture  of  clay  products  by  molding  stiff  tem- 
pered clay  in  a  continuous 
bar  and  wire  cutting,  the 
most  troublesome  defect 
and  the  greatest  weakness 
in  the  product  is  due  to 
laminations,  of  which  there 
are  two  well  recognized 
forms;  these  are  called 
auger  laminations  and  dif- 
ferential laminations. 

The    streams    or    strands 
of  clay  are  delivered  from 
the  auger  wings  in  helical 
Fi      1  form,  and  in  this  condition 


CLAYWORKING    PROBLEMS 


the  clay  is  forced  into  the  die.  The  strands  of  clay  are  imper- 
fectly welded  as  the  clay  passes  through  the  die,  thus  giving  a 
structure  similar  to  the  twisted  strands  of  a  rope.  Figure  1 
shows  the  center  or  core  taken  from  an  end-cut  brick  in 
which  the  two  twisted  strands  of  clay  from  the  auger  wings 
can  be  seen.  The  arrow  shows  the  direction  of  flow  of 
clay  in  passing  through  the  die. 

On  account  of  the  friction  of  the  clay  against  the  iron 
with  which  it  is  in  contact  the  clay  flows  at  a  greater  speed 
a't  the  center  of  its  stream,  resulting  in  a  structure  resembling 
overlapped  cones,  giving  what  is  called  a  differential  lam- 
inated structure.  The  overlapping  cone  or  differential  struc- 
ture can  be  best  studied  in  a  clay  column  issuing  from  a 
plunger  machine,  where  the  auger  laminations  are  entirely 
eliminated.  In  the  case  of  the  auger  machine  the  final  lami- 
na'ted  structure  is  the  result  of  the  combined  influences  of 
the  auger  and  differential  flow. 

One  method  of  reducing  auger  laminations  consists  of  an 
extension  provided  with  cross  bars  (Fig.  1)  placed  be- 
tween the  auger  and  the  die.  The  extension  with  its  cross  bars 
reduces  auger  laminations  in  two  ways.  First,  it  places  the 
die  farther  away  from  the  auger,  which  reduces  the  coiled 
structure,  but  at  the  same  time  increases  the  differential  lam- 
inating structure  and  decreases  the  velocity  of  flow  of  the 
column. 

The  cross  bars  break  up  !the  coils  as  they  leave  the  auger 
wings,  and  are  most  effective  when  placed  close  to  the  auger. 
If  the  bars  are  placed  too  close  to  the  die,  the  brick  may 
crack  or  separate  in  drying,  the  cracks  appearing  along  the 
planes  cut  by  the  cross  bars.  With  some  clays  it  seems 
impossible  to  use  a  cross  bar  or  core  bridge  between  the  die 
and  auger,  without  causing  the  ware  to  split  in  drying.  By 
placing  the  die  farther  away  from  the  end  of  the  auger,  and 
using  cross  cars,  the  auger  laminations  are  reduced,  velocity 
of  flow  reduced  and  differential  flow  increased.  The  closer 
the  die  is  placed  to  the  auger,  the  greater  is  the  velocity  of 


CLAYWORKING    PROBLEMS  81 

the  flow,  the  more  prominent  are  the  auger  laminations,  and 
the  less  apparent  is  the  differential  structure.  Auger  lami- 
nations are  far  more  troublesome  than  those  produced  by 
differential  flow,  as  can  be  verified  by  some  of  our  brick- 
making  friends  who  have  changed  from  the  old  plunger  ma- 
chine to  the  auger  type. 

Beside  auger  structure  there  is  considerable  differential 
structure  in  the  clay  on  passing  into  the  die.  The  laminated 
structure  in  the  clay,  as  it  enters  the  die,  cannot  be  de- 
stroyed as  it  passes  through  the  die,  but  it  can  be  modified 
by  the  manner  in  which  the  die  is  constructed  and  lubricated. 
If  a  die  be  insufficiently  lubricated,  the  friction  of  the 
clay  against  the  die  increases  the  differential  flow.  The  object 

of  lubrication  is  to 
reduce  friction,  and 
consequently  to  re- 
duce the  differential 
flow.  In  order  to  be 
most  effective,  lubri- 
cation should  be  in- 
Flg.  2  troduced  as  close  to 

the     intake     opening 

of  the  die  as  is  possible,  thus  not  only  overcoming  the  dif- 
ferential flow  which  would  otherwise  take  place  in  the  die, 
but  increasing  the  velocity  of  the  flow  of  the  clay  column. 
In  order  to  design  a  die  of  high  efficiency,  it  is  necessary 
to  understand  the  physical  behavor  of  clay,  and  the  funda- 
mental principles  of  lubrication.  For  the  present  purpose, 
stiff  tempered  clay  may  be  regarded  as  a  semi-fluid,  in 
which  an  applied  force  (AC)  at  a  given  point  (C)  in  Fig. 
2  is  transmitted  unequally  in  different  directions,  giving  ap- 
proximately an  elliptical  diagram  of  transmitted  pressures. 
The  transmitted  pressures  perpendicular  to  the  taper  lines, 
or  inside  face  of  the  die,  are  the  pressures  that  force  the 
clay  against  the  die  and  oppose  lubrication.  The  lubricating 
fluid,  in  order  to  be  effective,  must  then  be  admitted  to  the 


CLAYWORKING   PROBLEMS 


die  under  a  pressure  at  least  equal  to  the  opposing  force  of 
the   clay   against  'the   die. 

The  greater  the  taper  of  the  die,  the  greater  is  the  pressure 
opposing  lubrication.  Figure  3  is  an  illustration.  CD  and  EF 
represent  the  taper  lines  of  a  die.  The  transmitted  forces 
A  and  A  perpendicular  to  the  taper  lines  CD  and  EF  are 
the  forces  opposing  lubrication  at  these  points.  If  the  taper 
of  the  die  is  increased  so  that  GD  and  HF  become  the  taper 
lines,  then  forces  B  and  B  perpendicular  to  the  taper  lines 
are  in  opposition  to  the  lubricating  force.  Since  B  is  greater 


Fig.  3. 

than  A  it  follows  that  the  die  of  small  taper  requires  a  lower 
lubricating  pressure  than  the  die  of  larger  taper. 

The  lubricating  fluid  will  go  to  the  point  of  least  resistance. 
Therefore,  it  can  be  drawn  to  any  point  desired  in  'the  die, 
simply  by  reducing  the  taper  line  passing  through  that  point. 

Friction  is  greatest  in  the  die  at  the  corners  and  least  at 
the  middle,  'top  and  bottom.  It  is  desirable,  therefore,  to  re- 
lieve the  friction  at  the  corners  as  early  and  as  completely 
as  possible,  consequently  the  die  should  be  constructed  with 
the  smallest  taper  at  the  corners  and  greatest  'taper  at  the 
middle  top  and  bottom. 

The  proper  taper  lines   to  give  the   die   is   a   problem   de- 


CLAYWORKING    PROBLEMS 


s:; 


pending  upon  a  number  of  factors,  namely :  1.  Nature  of 
the  clay.  2.  Stiffness  of  temper.  3.  Capacity  of  molding 
machine.  4.  Amount  of  back  pressure  exerted  by  the  car- 
rier and  cutting  tables.  5.  Shape  of  the  column.  6.  Length 
of  die. 

From  practical  experience  it  has  been  found  under  normal 
working  conditions  that  the  variation  in  taper  at  the  middle, 
top  and  bottom  of  the  die  should  be  from  one-eighth  inch  to 
one-fourth  inch  to  the  foot,  and  the  taper  at  the  corners  less 
than  one-eighth  inch  to  the  foot,  for  dies  between  seven  and 
twelve  inches  in  effective  lengths. 

Short  clays,  stiff  tempered  clays,  molding  machines  of  high 
capacity,  high  back  pressure  and  long  dies  require  smaller 
tapers,  and  the  converse  of  these  conditions  requires  larger 
tapers. 

A  long  die  with  a  small  taper  per  linear  foot  gives  a 
much  better  column  than  a  short  die  with  a  larger  taper  per 


Fig.  4. 


r 

F 

Fig.  6. 

84  CLAYWORKING    PROBLEMS 

linear  foot.  This  is  especially  true  in  lubricated  dies  for 
large  capacity  machines. 

In  order  to  provide  for  lubrication  it  is  necessary  to  make 
the  die  in  sections  or  scales,  so  that  the  lubricant  can  pass 
through  and  moisten  'the  contact  surfaces  between  the  clay 
and  the  scales.  For  this  purpose,  two  or  more  scales 
are  necessary,  a  larger  number  being  preferable. 

By  making  extensive  experiments  in  applying  lubrication 
in  different  ways  the  best  results  were  obtained  by  the  fol- 
lowing me'thod :  Paper  gaskets  scant  one-thirty-second  of  an 
inch  thick  are  placed  between  the  scales.  The  gasket  nearest 
the  intake  die  opening  is  cut  out  at  the  top ;  the  other  gaskets 
make  the  contacts  between  the  scales  water  tight. 

The  lubricant  under  sufficient  pressure  can  pass  through 
and  around  the  column.  In  order  to  provide  channels 
for  the  lubricant  to  pass  around  the  column,  scales  of  the 
well-known  "offset"  type  are  used,  as  shown  in  Figure  4.  The 
lubricant  passes  through  at  A  to  the  offset,  or  channel  B, 
where  it  flows  around  the  column.  Since  the  die  taper  is 
least  at  'the  corners  the  lubricant  under  pressure  passes  for- 
ward by  way  of  the  corners  from  B  to  the  offset  C  in  the 
succeeding  scale.  Here  the  lubricant  also  flows  around  the 
column  and  proceeds  in  the  same  manner  of  successive 
offsets. 

When  water  is  used  and  the  die  is  lubricating  under  proper 
water  pressure  and  volume  a  little  wa'ter  can  be  seen  oozing 
out  at  the  corners  of  the  die.  If  the  water  is  admitted  to 
the  die  under  too  low  a  pressure  lubrication  is  shut  off  and 
the  column  cracks.  If  the  waiter  pressure  and  volume  are 
too  great  water  is  forced  into  the  weakest  spots  in  the  column, 
giving  water  marks,  so  that  it  is  essential  to  provide  a  suit- 
able pressure  regulator  for  regula'ting  the  water  pressure 
to  the  right  degree. 

Since  the  greatest  taper  of  the  die  should  be  farthest  from 
the  corners  and  the  smallest  taper  at  the  corners  the  shapes 
of  'the  intake  and  outlet  openings  for  the  rectangular  die 


CLAYWORKING    PROBLEMS  85 

would  be  similar  to  the  diagram  shown  in  Figure  5.  The 
position  of  the  observer  is  behind  the  die,  looking  through  it 
in  the  direction  in  which  the  clay  is  flowing.  The  outer  lines 
represent  the  intake  opening  and  the  inner  rectangle,  the 
outle*t  opening.  A  particle  of  clay  moving  from  point  A 
of  ingress  to  point  B  of  egress  passes  on  the  line  of  great- 
est taper,  while  four  clay  particles,  one  moving  through 
the  die  at  each  of  the  four  corners  cccc  would  be  in  parallel 
motion  along  lines  of  least  taper.  As  the  clay  moves  through 
the  die  each  successive  scale  acts  upon  the  forming  column 
and  gradually  changes  it  from  the  form  it  takes  on  enter- 
ing the  die  to  the  final  form  on  issuing  from  the  die. 

The  pressure  of  the  clay  is  greatest  along  the  greatest 
taper  line,  AB,  consequently  the  water  would  flow  for- 
ward along  the  lines  of  least  taper  at  the  corners  to  the 
succeeding  offsets  in  the  scales,  each  offset  serving  as  a  reser- 
voir to  hold  some  of  the  water.  On  removing  a  die  from 
the  machine  and  carefully  cleaning  out  the  clay  the  offsets  of 
the  scales  were  found  to  be  filled  with  a  soft,  plastic  slip, 
which  is  the  real  lubricant. 


Water  vs.  Steam  Lubrication 

594.  Ontario — What  is  your  opinion  of  water  lubrication 
for  the  dies  of  a  brick  machine,  in  comparison  to  steam?  We 

have  a machine  with  ordinary  lubricating  die  and  a 

•water  supply  from  a  tank  of  approximately  1,000  gals.,  at  an 
elevation  of  twenty  feet  above  the  machine  and  almost  direct- 
ly above  it.  The  material  is  a  very  fine-textured  lime  .clay. 

On  a  few  plants  that  have  changed  over  from  steam  to  elec- 
tricity, thereby  cutting  off  the  supply  of  steam  for  lubricating 
purposes,  it  has  been  found  necessary  to  use  water  lubrica- 
tion under  pressure.  In  a  few  cases,  it  has  been  successful, 
but  these  cases  are  rare — so  rare  as  to  make  it  easy  to  say 
that  success  would  have  been  attained  with  a  perfectly  dry 
die.  To  get  perfect  lubrication  by  use  of  water  under  water- 


86  CLAYWORKING    PROBLEMS 


column  pressure  is  difficult.  The  lubricating  rings  become 
clogged,  with  resultant  "splotch"  lubrication  or  none  at  all — 
or  the  opposite  happens,  that  so  much  water  is  supplied  that 
the  column  is  flooded  and  the  faces  and  corners  of  the  bar  are 
made  "soggy."  This  sogginess  not  only  produces  uneven 
faces,  but  the  brick  are  apt  to  bond  together  when  hacked 
on  the  dryer  cars.  In  steam  lubrication  it  is  advisable  to 
so  regulate  the  pressure  that  the  die  is  heated,  without  al- 
lowing the  vapor  to  escape.  The  lubricating  effect  of  the 
steam,  in  the  form  of  water,  and  the  formation  of  steam  on 
the  bar  of  clay  as  it  passes  through  the  liner  section  of  the 
die,  certainly  is  superior  to  water  lubrication.  Why  not  try 
a  small  auxiliary  boiler?  A  pressure  as  low  as  five  pounds 
will  be  sufficient. 


CLAYWORKING    PROBLEMS  87 


CHAPTER  IV 

WHICH    DEALS    WITH    A    MULTITUDE 
OF  QUESTIONS 

As  to  Car  Shipments  of  Clay 

586.  Tennessee — Can  a  common  brick  plant  of  75,000  daily 
capacity,  be  operated  successfully  if  the  clay  must  be  shipped 
from  the  pit  to  the  plant  by  rail?  In  my  case  the  clay  is 
harvested  by  a  steam  shozel  and  by  it,  is  loaded  on  freight 
cars.  The  distance  front  the  plant  to  the  pit  is  about  three 
miles  and  the  switching  charges  are  $5.00  per  car. 

So  many  factors  enter  into  the  "successful"  operation  of 
a  brick  plant  that  the  above  question  is  not  easy  to  answer. 
Assuming  that  our  correspondent  has  a  market  which  takes 
the  entire  output  at  an  average  price,  and  that  his  cost  of 
production,  after  the  clay  has  reached  the  grinding,  is  prac- 
tically the  same  as  that  of  an  average  plant,  we  would  say 
that  the  switching  charge  of  $5.00  per  car  would  not  make 
his  project  a  failure.  It  would,  however,  materially  reduce 
his  profits,  in  that  it  would  increase  his  cost.  We  would  be 
glad  if  our  readers  would  answer  the  question  printed  above. 
For  the  sake  of  getting  some  comparative  figures  that  will 
be  of  value  to  our  subscriber,  we  would  ask  that  our  read- 
ers give  us  some  facts  regarding  the  cost  of  transporting 
clay  from  their  clay  pits  to  their  machine  rooms,  which 
would  include  every  cost  from,  the  point  that  the  clay  was 
loaded  into  some  kind  of  a  conveyor  up  to  the  time  it 
actually  reached  the  bin  or  floor  adjacent  to  the  pugmill  or 
crushing  device,  this  to  be  compared  to  our  subscribers' 
cost  of  $5.00  per  car,  and  assuming  that  his  "cars"  are 


88  CLAYWORKING    PROBLEMS 


ordinary  railroad  gondolas.  We  must,  however,  add  to  this 
$5.00  per  car  charge,  his  cost  of  unloading  the  clay  from 
the  car  into  the  storage  bin.  C.  O.  Arbogust  states  that  he 
knows  of  only  one  concern  that  has  its  clay  shipped  to  it  by 
railroad  and  which  uses  this  method  of  securing  clay  for  the 
manufacture  of  common  brick.  This  is  the  Hydraulic-Press 
Brick  Company  of  St.  Louis,  Mo.,  which  ships  clay  to  five 
St.  Louis  plants,  5,  11,  3,  4  and  Union  yard,  by  means  of 
hopper  gondolas.  The  clay  and  shale  is  loaded  by  clamshell 
and  steam-shovel  at  the  pits,  which  are  located  at  Malcolm, 
Mo.,  about  twelve  miles  west  of  St.  Louis.  Each  car  is 
equipped  with  two  bottom  dump  trap  doors  from  which  the 
shale  falls  into  hoppers  over  spiral  clay  feeders  which  in 
turn  feed  directly  into  the  pans.  Storage  room  is  also  pro- 
vided and  the  clay  is  shoveled  by  hand  from  the  cars  into 
this  shed,  from  which  it  is  fed  to  the  pan  by  wheelbarrows. 
The  Hydraulic-Press  Brick  Company  could  not  sustain  the 
excess  cost  of  this  manner  of  transporting  its  clay  if  it  did 
not,  as  noted,  supply  five  plants,  which  make  approximately 
400,000  brick  per  day.  At  that,  the  clay  shipped  in  and  util- 
ized in  the  manufacture  of  common  brick  is  only  about  30 
per  cent  of  the  total.  The  average  standard  size  gondola 
contains  enough  clay  to  make  approximately  18,000  brick. 

The  Cost  of  Natural  Gas  Fuel 

501.  Ohio — We  arc  about  to  install  a  gas  burning  equip- 
ment in  our  kilns,  which  arc  round,  being  thirty  feet  in  diam- 
eter. Can  this  style  of  kiln  be  burned  successfully  with  gas 
and  how  does  the  cost  of  this  type  of  fuel  compare  with  the 
cost  of  bunting  zi'ith  coal?  We  arc  now  paying  $1.25  per  ton 
for  coal  and  gas  as  thirteen  cents  per  thousand  cubic  feet.  We 
arc  making  a  soft  mud  brick  Zi'cighing  four  and  one-half 
pounds  apiece. 

Almost  any  type  of  kiln  can  be  used  for  natural  gas  burn- 
ing. But  the  economy  of  using  this  form  of  fuel  and  of 


CLAYWORKING    PROBLEMS  89 

paying  the  price  you  name  for  it,  to  burn  soft  mud  common 
brick,  is  very  doubtful. 

The  heating  value  of  one  cubic  foot  of  natural  gas  is  ap- 
proximately one  thousand  B.  T.  U.  and  that  of  one  pound 
of  bituminous  coal  averages  near  fourteen  thousand  five  hun- 
dred B.  T.  U.  Therefore,  a  ton  of  coal  which  costs  $1.25 
gives  about  twenty-nine  million  B.  T.  U.,  while  the  same 
amount  of  money  spent  for  natural  gas  at  thirteen  cents  per 
thousand  cubic  feet  gives  only  about  ten  million  B.  T.  U. 

Allowing  thirty  cents  per  ton  for  labor,  depreciation  and 
interest,  the  cost  of  natural  gas  as  a  fuel  is  equal  to  coal  if, 
for  instance,  one  ton  of  coal  costs  $1.25  and  one  thousand 
cubic  feet  of  natural  gas  seven  cents.  But  it  is  our  opinion 
that  natural  gas  at  thirteen  cents  per  thousand  cubic  feet  is 
too  expensive  for  the  burning  of  soft  mud  common  brick. 


Cost  of  Electric  Power  Per  Thousand  Brick 

330.  New  York — What  is  the  cost  of  electric  power  per 
thousand  for  soft  mud  brickf  We  have  a  Wellington  Mon- 
arch machine  of  30.000  daily  capacity,  and  as  we  have  been 
paying  from  2J/^c  to  2l/$c  per  kw.-hour,  our  brick,  which  is 
soft-mud,  costs  us  20c  per  thousand  for  power  on  our  ma- 
chine. As  the  power  company  has  advanced  the  rates  tve 
want  to  use  these  comparative  figures  for  the  purpose  of  try- 
ing to  get  a  reduction.  What  is  the  usual  power  cost  to  make 
one  thousand  brick  on  one  machine,  giving  the  figures  per 
kw.-hour  as  well  as  the  cost  per  Mi 

We  have  communicated  with  several  plants  operating  un- 
der similar  conditions  but  have  received  but  two  replies. 
Hilker  Bros.  Brick  Mfg.  Co.,  Racine,  Wis.,  write: 

"We  are  using  a  Pott's  soft-mud  machine  and  are  making 
24,000  brick  per  8  hours  per  day.  We  are  using  a  pugmill, 
and  a  disintegrator  and  a  winding  drum  to  haul  the  clay 
from  the  clay  pit,  we  also  have  a  conveyor  500  feet  long 


90  CLAYWORKING    PROBLEMS 


to  carry  the  mould  along  the  yard.  This  machinery  is  all 
driven  by  one  engine.  We  use  steam  power  and  we  use 
about  three-fourths  ton  of  coal  per  day,  which  costs  us  $3 
per  ton  delivered  at  our  boiler  room,  so  that  would  cost  us 
about  .bo*/*  cents  per  thousand  for  coal  and,  figuring  about 
.03  cents  for  oil  for  engine,  so  that  would  make  our  cost 
per  thousand  brick  about  .12]/>  cents  for  power.  This  is  what 
we  suppose  your  subscriber  in  New  York  wants  to  know." 

Voelker  &  Groff,  proprietors  of  the  Winona  Brick  Yards, 
Winona,  Minn.,  write : 

"Our  conditions  are  somewhat  different  than  your  sub- 
scriber's. We  run  our  Wellington  Monarch  machine  with 
one  motor  and  cable  conveying  machine  with  another  moto/ 
pumping  water  with  another  large  motor  on  our  drag  line 
scraper  for  scraping  our  clay  motor  on  centrifugal  pump  for 
pumping  water  out  of  clay  bank.  We  pay  for  our  power  by 
a  sliding  scale.  The  minimum  charge  is  2^  cents  per  kilo- 
watt. Our  power  costs  us  0.234  per  M.  brick." 


Cost  of  Electric  Current 

353.  Nebraska— How  much  per  kilowatt  does  electric  cur- 
rent cost  at  brick  plants  bought  from  power  stations,  cither 
municipal  or  private,  generated  by  steam  power?  We  hare 
electric  drive  but  believe  our  price  for  current  is  high.  We 
run  a  Fate  bottom  dump  car,  standard  size;  Fate  linnding 
drum,  American  Clay  Machinery  Co.  18-inch  disintegrator,  44- 
ft.  conveyor,  7-foot  pug  mill,  a  No.  218  American  Clay  Ma- 
chinery Co.  machine  and  cutting  table,  making  brick  or  block. 
IV c  use  on  an  average  40  kilowatts  an  hour,  making  about  an 
average  of  4,000  common  brick  per  hour,  or  1,000  5x8x12 
block.  This  average  of  pozccr  varies  some.  It  takes  more  if 
the  clay  is  worked  somewhat  stiff.  We  have  a  sliding  scale 
on  electricity  from  6  to  7  cents  down  to  4  cents  per  kilowatt. 


CLAYWORKING    PROBLEMS  91 

We  hare  a  100-/J.  p.  Westinghouse  motor,  2,200  volts  alter- 
nating current. 

Local  conditions  and  the  nature  of  the  clay  are  sometimes 
determining  factors  in  the  amount  of  current  necessary  per 
thousand  brick.  Likewise  these  things  deterimne  costs.  The 
Albany  Brick  Company,  Albany,  Ore.,  operates  a  Potts  dis- 
integrator with  clay  elevator,  one  8-ft.  clay  pug  mill,  Bucyrus 
Acme  brick  machine,  capacity  25,000  per  day.  During  the 
period  of  four  months  operation  the  average  kilowatt-hours 
per  thousand  of  brick  made  was  8.16.  We  do  not  know  the 
rate  of  power  but  if  you  figured  2J/2  cents  per  kilowatt-hour, 
the  cost  per  thousand  is  slightly  over  20  cents.  The  Enid 
Vitrified  Brick  &  Tile  Company,  Enid,  Okla.,  are  using  a 
motor  for  operating  one  9-ft.  dry  pan,  one  mixer,  a  six-mold 
brick  machine,  capacity  30,000  per  10  hours,  one  2.000-lb. 
hoist  elevator  and  conveyors.  Tests  made  on  this  plant  show 
11.2  kilowatt-hours  per  1,000  brick. 


Clay  Haulage  from  Pit 

74.  Ontario — Can  you  tell  me  where  I  can  find  information 
in  regards  to  hauling  clay  from  pit  to  factory  a  distance  of 
800  //.  or  possibly  1.000  ft.?  How  much  could  a  horse  pull 
on  a  level  tramway  per  day?  Could  it  pull  enough  for  60,000 
common  building  brick f  U'ould  this  distance  be  too  long  for 
a  drum  and  cable  haulage  and  what  grade  would  be  necessary 
to  allow  car  to  run  back  empty  to  pit  if  we  used  reversible 
engine?  Any  information  will  be  appreciated  on  tramminy 
or  hauling  of  clay  from  pit  to  plant  as  to  amount  hauled  in  a 
day  and  grading  of  tramway  such  as  would  give  horse  advan- 
tage in  pulling  load. 

The  average  speed  of  a  horse  walking  is  supposed  to  be 
from  2  to  2J4  miles  per  hour,  or  about  176  to  196  ft.  per  min- 
ute. Taking  the  lowest  figure  of  the  two,  and  based  upon  a 
distance  of  1,000  ft.  from  clay  pit  to  plant,  a  horse  would 
require  about  11 1/2  minutes  actual  travel.  Allowing  y/2  min- 


92 CLAYWORKING   PROBLEMS 

utes  for  delays  at  each  end,  about  15  minutes  would  be  re- 
quired for  a  round-trip,  or  an  average  of  4  trips  per  hour. 

Upon  a  basis  of  60,000  brick,  of  an  average  weight  of  4JX 
Ibs.  each,  the  daily  capacity  required  would  be  about  135 
tons  per  day,  or  15  tons  per  hour,  estimated  upon  a  9-hour 
day. 

From  the  above  it  can  be  seen  that  it  would  be  necessary 
to  carry  7,500  Ibs.  of  clay  per  trip,  which  would  be  two  1JX 
yd.  cars,  or  three  1-yd.  cars.  The  weight  of  these  cars  load- 
ed would  probably  amount  to  at  least  10,000  Ibs.,  or  5  tons. 

We  would  say  that  the  rolling  friction  for  industrial  cars 
as  used  for  this  work,  would  be  about  40  Ibs.  per  ton.  A  5- 
ton  load  on  level  track  would,  therefore,  require  a  pull  oi 
approximately  200  Ibs.  The  tractive  power  of  the  ordinary 
horse  would  average  from  100  to  125  Ibs.  By  having  a  down- 
grade from  pit  to  plant,  of  1  to  ll/2  per  cent,  it  might  be 
possible  for  a  horse  to  do  this  work  but  we  doubt  very  much 
if  it  would  be  at  all  satisfactory,  especially  in  bad  weather. 

By  far,  the  most  practical  and  economical  arrangement 
would  be  to  install  a  surface  haulage  system,  in  which  the 
cars  are  pulled  one  or  both  ways,  by  wire  rope.  In  the  event 
the  grade  from  plant  to  pit  could  be  made  sufficient  to  re- 
turn empty  cars  by  gravity,  only  single  rope  and  hoisting 
drum  would  be  required.  If,  on  the  other  hand,  the  grade 
is  not  sufficient  to  return  the  empty  cars  by  gravity,  the  tail^ 
rope  system  would  have  to  be  used,  whereby  the  empty  cars 
would  be  returned  by  a  small  cable  or  tail  rope.  Just  what 
grade  would  be  needed  to  return  the  empty  cars  by  gravity 
would  vary  according  to  the  type  of  bearings  used  on  the 
cars,  six  of  truck  wheels,  and  condition  of  track.  For  data 
on  this  point,  we  would  suggest  that  you  write  manufacturers. 

Whether  the  aerial  tramways  such  as  are  manufactured  by 
one  of  our  advertisers  will  meet  your  requirements,  depends 
entirely  upon  local  conditions.  With  an  aerial  tramway 
economical  results  can  only  be  obtained  where  the  clay  is 


CLAYWORKING    PROBLEMS  93 

brought  to  a  central  loading  station  for  loading  into  tramway 
buckets.  With  a  two-bucket  or  jig-back  system  with  power- 
drive  located  at  loading  station,  but  one  attendant  would  be 
required  for  the  entire  operation  of  the  tramway.  This  man 
would  be  located  at  the  loading  station,  and  control  the  filling 
of  buckets  as  well  as  the  power  and  speed  of  line. 


How  to  Keep  Coal  Out  of  Fire  Clay 

241.  Ohio — We  have  a  small  vein  of  coal  lying  above  our 
clay  and  hare  great  difficulty  in  getting  the  miners  to  keep 
the  coal  out  of  the  cars  in  which  they  send  the  clay  to  the 
tipple.  As  the  lumps  of  coal  are  comparatively  small,  and 
generally  buried  in  the  car,  they  are  not  discoi-ered  until  the 
clay  is  put  into  the  dry-pan.  If  it  is  not  eliminated  at  this 
point,  it  is  ground  up  and  goes  into  the  brick,  where  it  later 
burns  out  and  pits  the  product.  It  seems  impossible  to  fasten 
the  blame  on  any  one  miner. 

If  the  coal  vein  is  large  enough  to  be  an  inducement,  try 
the  plan  of  offering  it  free  of  charge,  to  the  men  that  work 
in  the  mine.  Arrange  matters  so  that  it  will  be  kept  separate 
in  the  workings,  the  men  understanding  that  they  are  saving 
something  that  is  of  value  to  themselves,  and  they  may  be 
depended  upon  not  to  mix  any  clay  with  the  coal  that  is  to 
go  into  their  own  stoves.  When  a  single  carload  has  been 
accumulated  in  any  one  of  the  workings,  the  miner  can  load 
it  out,  marking  the  car  in  some  way  that  will  enable  the  man 
at  the  tipple  to  readily  identify  it  and  to  side-track  it  to  a 
private  coal  dump,  which  will  belong  to  the  men.  Give  them 
to  understand  that  they  are  at  liberty  to  send  carts  to  this 
dump  and  to  take  away  all  the  coal  they  need  for  their  own 
household  use,  free  of  charge.  In  their  effort  to  accumulate 
enough  free  coal  to  supply  their  own  wants,  they  will  keep  it 


CLAYWORKING    PROBLEMS 


out  of  the  clay  cars,  even  though,  by  doing  so,  they  may  be 
using  up  some  time  that  they  think  should  be  paid  for. 


Amortization  of   Bank  Indebtedness 

243.  Tennessee — 1 1' hat  is  the  meaning  of  amortization,  as 
applied  to  bank  indebtedness?  I  heard  a  lecturer  use  the  term 
and  from  what  he  said,  think  he  beliei'cd  it  to  be  a  panacea 
for  all  industries  that  were  handicapped  by  amounts  due  to 
local  banks,  particularly  short  time  notes. 

Webster  defines  amortize  as  follows :  "To  extinguish,  as 
a  debt,  usually  by  means  of  a  sinking  fund."  This  is,  we 
admit,  not  very  enlightening.  The  process  of  amortization, 
as  pursued  in  France  (where  it  is  extensively  used  in  con- 
nection with  farm  mortgages),  is  very  simple.  Let  us  sup- 
pose that  the  mortgage  is  for  $1,000,  and  bears  quarterly 
interest  of  !}/>  per  cent.  The  borrower,  under  ordinary  con- 
ditions, would  pay  $15.00  every  three  months,  and,  when  the 
mortgage  came  due,  would  still  owe  the  $1,000.  The  prin- 
ciple of  amortization  would  be  applied,  if  the  borrower 
made  arrangements  whereby  he  could  pay,  say  2l/2  per 
cent  quarterly,  or  $25.00.  At  the  end  of  the  first  quarter, 
having  made  this  payment,  he  would  owe  $990.00.  One-and- 
one-half  per  cent  on  that  amount  would  be  $14.85.  At  the 
end  of  the  second  quarter,  paying  $25.00  would  reduce  the 
amount  of  the  mortgage  to  $979.85.  Add  interest  to  this,  as 
before,  and  pay  $25.00  at  the  end  of  the  third  quarter,  and 
the  indebtedness  would  be  $969.54.  At  the  end  of  the  first 
year,  the  payment  of  $25.00  would  make  the  indebtedness 
$959.08.  From  this  it  will  be  seen  that  while  $40.00  -has  been 
paid  back  in  four  installments  of  $10.00  each,  the  indebtedness 
has  been  reduced  92c  representing  the  interest  earned.  The 
idea  is,  that  the  amounts  paid  back  are  so  small  that  they 
will  not  embarrass  the  debtor,  but,  if  persisted  in,  will  event- 
ually wipe  out  the  original  debt.  When  the  same  plan  is 


CLAYWORKING    PROBLEMS  95 

tried  with  notes,  it  works  very  smoothly,  for,  as  the  note  is 
renewed,  the  check  for  the  interest,  plus  the  amortization 
amount,  is  given  at  the  same  time  as  the  renewal  note,  with 
the  amount  of  the  latter  a  little  less  each  time,  than  the 
amount  of  the  note  that  is  being  taken  up. 


Methods  of  Washing  Fire  Clay 

562.  Tennessee — Will  you  please  gire  us  a  description  of 
the  best  known  method  and  appliances  for  washing  fire  clay 
to  rid  it  of  chert  (flint)  and  impurities.  In  our  clay  there  is 
about  ten  per  cent  chert  ranging  from  pea  to  walnut  size. 
We  should  like  to  recover  the  chert  for  other  purposes.  Also 
please  refer  us  to  the  best  literature  covering  this  subject. 

The  methods  of  purifying  fire  clay  depend  upon  the  phys- 
ical character  of  the  clay,  its  value  and  upon  the  degree  of 
purification  required.  Your  clay  may  be  a  loose  material 
like  the  so-called  "kaolins"  (micaceous  sands)  of  New  Jer- 
sey, or  it  may  be  an  earthy  or  a  tough,  plastic  clay,  like  some 
of  the  fire  clays  of  New  Jersey,  kaolin  in  Pennsylvania,  crop 
No.  2  fire  clays  of  the  coal  measures,  kaolins  of  Georgia, 
Alabama  and  Arkansas,  fire  clays  of  Texas,  or  it  may  be 
rock-like,  such  as  the  solid  No.  2  fire  clays  of  the  coal  meas- 
ures, or  finally,  it  may  be  non-plastic  flint  clay  like  that  of 
Pennsylvania.  Maryland.  Ohio  and  Kentucky.  No  single 
method  of  purification  would  be  applicable  to  these  several 
varieties  of  clay. 

Kaolins  are  washed  by  beating  them  to  a  thin  pulp  or  slip 
in  a  pug  mill  or  granulator  type  of  machine,  or  a  blunger; 
the  course  materials  may  be  eliminated  in  a  sand  wheel  or 
sand  box ;  the  fine,  slow-setting  impurities,  such  as  mica,  are 
removed  in  settling  or  flotation  troughs,  and  the  creamy  kaolin 
slip  is  collected  in  settling  tanks.  After  settling,  the  sur- 
plus water  is  drawn  off  and  the  remaining  slurry  is  pumped 


96  CLAYWORKING   PROBLEMS 


into  filter  presses.  The  filter  press  cakes  are  air  dried  in 
sheds  or  artificially  dried  in  some  type  of  dryer. 

Some  low  grade  pottery  (including  stoneware)  clays  are 
simply  beaten  up  and  brought  into  suspension  in  a  blunger, 
followed  by  screening.  The  slip  which  passes  through  the 
screen  is  collected  in  a  tank  or  cistern  and  kept  in  suspension 
by  a  stirring  mechanism  (agitator)  until  it  can  be  pumped 
to  the  filter  presses.  The  cakes  from  the  filter  press  are 
passed  through  a  potter's  pug  mill  and  the  pugged  material 
taken  directly  to  the  potter  or  stored  in  damp  cellars. 

Obviously  this  method  of  purification  would  be  too  ex- 
pensive for  a  low  grade  fire  clay  to  be  used  in  the  manu- 
facture of  brick  or  other  low  priced  wares.  It  might  be  prac- 
tical to  blunge  the  clay,  screen  out  the  stones  and  collect 
the  screened  slip  in  open  tanks  or  basins  from  which  the  sur- 
plus water  could  be  drained  off  after  the  clay  had  settled, 
then  allow  the  clay  mass  to  air  dry  until  stiff  enough  to  handle. 
If  the  clay  is  very  loose  and  friable,  instead  of  blunging,  it 
could  be  washed  through  a  screen  following  the  method  used 
in  washing  gravel,  but  there  still  remains  the  removal  of  the 
excess  water  and  subsequent  drying  to  be  taken  care  of. 

If  the  clay  is  friable  and  dry,  or  after  drying,  it  could  be 
whipped  into  a  powder  and  passed  over  a  screen.  The  courser 
material,  including  the  flint  pebbles,  in  this  case,  would  pass 
over  the  screen  while  the  clay  would  collect  in  a  bin  under  the 
screen.  The  separation,  using  this  method,  however,  would 
not  be  complete,  since  the  fine  pieces  of  flint  would  follow 
the  clay  while  course  masses  of  clay  would  collect  with  the 
flint.  This  dry  method  of  separating  the  pebbles  from  the 
clay  has  been  successfully  used  in  a  number  of  cases.  For 
instance,  we  have  seen  a  somewhat  similar  dry  separation  car- 
ried on  in  a  dry  pan  with  raised  mullers  in  several  factories. 
Thus  the  mullers  would  not  crush  the  stones  but  simply  loosen 
them  from  the  clay.  The  fine  clay  would  pass  through  the 
perforated  plates,  while  the  stones  would  remain  in  the  pan. 
At  frequent  intervals,  the  pan  would  be  stopped  or  slowed 


CLAYWORKING   PROBLEMS  97 


down  and  the  stones  removed.  A  very  powdery  clay  could 
be  whipped  to  dust  without  in  any  way  reducing  the  size  of 
the  stone  and  could  then  be  separated  from  the  stones  by 
an  air  blast  similar  to  the  method  employed  in  preparing  clays 
for  dry  pressed  tile. 

If  the  clay  is  a  tough,  plastic  material,  it  can  best  be  cleaned 
in  a  Diesner  cleaner.  In  this  operation  the  clay  is  pugged  in 
an  ordinary  mill  and  put  through  an  auger  machine.  The 
bar  of  clay  from  the  machine  is  forced  against  a  vertical  re- 
volving slotted  disc,  the  fine  clay  passing  through  the  slot 
while  the  stones  are  rejected.  The  resulting  mass  is  in  con- 
dition for  immediate  manufacture  into  ware,  but  the  stones 
would  have  considerable  clay  mixed  with  them  and  would 
have  to  be  washed,  which  could  readily  be  done. 

We  do  not  know  of  any  publication  covering  this  subject. 
In  the  earlier  reports  of  the  National  Brick  Manufacturers' 
Association  will  be  found  a  description  of  a  "slumming" 
process  for  common  clays  in  which  you  might  be  interested. 
Bulletin  No.  53,  Mineral  Technology  No.  1,  Bureau  of  Mines, 
Mining  and  Treatment  of  Feldspar  and  Kaolin  in  the  South- 
ern Appalachian  Region,  by  A.  S.  Watts,  which,  it  is  pos- 
sible, might  be  secured  from  the  Director,  Bureau  of  Mines, 
Washington,  describes  kaolin  washing  in  that  field. 


Wants  to  "Copyright"  Trade  Name 

593.  Missouri — We  have  a  brand  of  brick  which  we  hare 
been  manufacturing  for  about  ten  years,  and  it  is  of  such 
quality  that  it  has  made  quite  a  reputation  for  us.  We  have 
been  selling  it  under  this  brand  for  probably  ten  or  eleven 
years.  We  notice  that  lately  one  or  two  other  fire-brick  com- 
panies are  manufacturing  a  brick  under  the  same  brand.  We 
think  we  are  the  first  who  have  used  this  brand,  and  thought 
it  might  be  well  to  protect  ourselves  by  U.  S.  copyright.  We 
hare  never  heard  of  any  other  brick  being  copyrighted  by  the 
same  title  as  ours,  and  none  is  shown  in  your  list.  What  we 


CLAYWORKING    PROBLEMS 


would  like  to  know  is,  should  we  have  the  name  copyrighted 
as  a  trade  mark,  would  we  not  have  preccd  :ice  over  anyone 
else,  even  though  we  might  not  have  first  used  it?  Our  im- 
pression is  that  we  arc  the  first.  Do  you  know  the  probable 
cost  of  copyrighting  a  trade  mark? 

The  general  practice  is  to  register  the  name  in  the  United 
States  Patent  Office.  The  cost  of  this  will  be  something  in 
the  neighborhood  of  $25  or  $30. 

Ordinarily,  patent  office  registration  is  not  granted  upon 
any  name  or  word  which  is  either  descriptive  or  geographical. 
An  exception  is  made,  however,  when  the  name  or  word  has 
been  in  continuous  use  for  more  than  ten  years. 


Mortar   Joints   for   Interior   Brickwork 

120.  Illinois — We  have  a  customer  who  is  contemplating  the 
decoration  of  an  interior  room  with  rough  surfaced  face-brick. 
Can  you  give  us  any  information  in  regard  to  the  size  and 
style  of  mortar  joints? 

Width,  grain,  finish  and  color  are  the  four  factors  in  mor- 
tar joints  that  determine  the  texture  of  the  finished  brickwork. 
Width  and  color  are  the  two  factors  that  determine  the  gen- 
eral color-tone.  The  influence  of  the  width  of  the  joint  on 
the  finished  work  can  be  appreciated  when  it  is  understood 
that,  with  a  brick  2l/4  in.  thick,  a  quarter-inch  joint  constitutes 
10  per  cent  and  a  half-inch  joint  18  per  cent  of  the  finished 
wall  surface.  So  the  design  of  the  brick  work  and  the  color 
of  the  mortar  that  is  to  be  used  must  both  be  taken  into  con- 
sideration in  fixing  the  width  of  the  joint.  It  is  a  question  of 
weaving  an  imperishable  fabric  with  threads  of  varying  thick- 
ness, the  brick  being  of  one  measurement,  the  joint  an- 
other. 

Harmony  of  the  surface,  so  that  each  plane  of  the  finished 
work  will  give  back  the  same  light,  demands  that  the  grain  of 
the  joint  should  be  the  same  as  the  grain  of  the  brick— that  is, 
of  equal  coarseness.  This  is  given  by  adding  gravel  to  the 


CLAYWORKING  PROBLEMS 


sand  used  in  the  mortar,  a  good  formula  being  10  parts  sharp 
building  sand,  4  parts  gravel,  2  parts  Portland  cement  and  1 
part  lime  putty.  The  gravel  should  be  through  a  quarter- 
inch  mesh  screen.  On  account  of  the  large  proportion  of 
cement  in  this  formula,  it  is  necessary  to  use  more  coloring 
matter  than  would  be  used  in  lime  mortar  and  the  mistake 
that  most  builders  make  is  to  accept  the  color  of  the  wet  mor- 
tar with  the  feeling  that  "it  will  dry  out  a  little  lighter" — 
the  fact  is  that  "it"  dries  out  a  great  deal  lighter,  and  a  good 
rule  for  interior  work  is  to  put  in  "enough"  mortar  color  and 
then  put  in  about  half  as  much  again. 

If  the  mortar  is  mixed  properly  and  only  enough  water  add- 
ed to  make  it  work  stiffly,  it  will  not  run  down  over  the  sur- 
face of  the  brick.  Remember,  mortar  stains  on  rough  finished 
face  brick  are  very  hard  to  remove.  It  should  feel  "rubbery" 
to  the  trowel  and,  if  the  bricklayer  has  not  laid  up  rough 
finished  face-brick  in  interior  work  before,  he  will  be  apt 
to  object  to  the  extra  "poorness"  of  the  mortar.  If  he  does 
not  "kick" — lookout — the  mortar  is  too  fluid  and  will  be  apt 
to  soil  the  work. 

Finish  the  joints  either  "rough  struck  flush"  by  striking 
up  with  the  edge  of  the  trowel,  in  the  same  way  as  com- 
mon backing  up  work  is  struck,  or  "rake"  with  a  wooden 
"Dutchman."  This  latter  is  a  wedge  shaped  piece  of  wood, 
the  edge  being  slightly  narrower  than  the  width  of  the  joint. 
The  soft  wood  leaves  a  surface  on  the  joint  that  is  immeas- 
urably superior  to  the  surface  left  by  any  metal  jointing  tool. 

The  color  must  be  chosen  with  relation  to  the  color  of  the 
brick  and  to  the  color-tone  of  the  finished  work.  The  for- 
mula given  above  produces  a  grayish-white  joint  and  is  made 
warmer  by  the  addition  of  enough  yellow  ochre  to  make  the 
wet  mortar  a  deep  lemon.  This  will  dry  out  a  rich  cream. 
By  adding  half  double-strength  brown  and  half  black,  a  dark 
brown  is  obtained  in  the  wet  mortar,  that  changes,  through 
the  action  of  the  cement,  to  a  grayish-purple  when  the  joint 
is  thoroughly  dry.  Do  not  use  black  alone,  in  any  mortar  to 


100  CLAYWORKING  PROBLEMS 

which  cement  is  added,  as  the  latter  forms  a  film  around  the 
black  particles  and  turns  them  to  a  whitish-blue  in  spots 
where  the  moisture  has  been  greatest.  Any  of  these  joints 
are  good  for  shale  brick — half  brown  and  half  yellow  color 
is  excellent  for  fire  clay  brick  in  shades  from  orange  to  dark 
brown.  Do  not  use  red  color  alone.  Add  some  black  to  your 
white  mortar,  if  no  cement  is  used  and  so  "vaccinate"  against 
the  dinginess  of  the  joint  as  dust  and  dirt  accumulate. 


Imitation  "Harvard"  Headers 

123.  New t  York — We  manufacture  red  building  brick,  by 
the  soft  mud  process,  and  would  like  to  make  some  black  end 
brick,  commonly  known  as  "Harvard"  headers:  Can  you  give 
us  any  information  as  to  how  to  make  them?  We  thought 
that  by  dipping  green  brick  in  some  chemical  solution  and 
then  burning,  we  might  produce  the  black  end. 

We  do  not  know  of  a  single  instance  where  the  "Har- 
vard" greenish-black,  wrinkled  header  has  been  produced 
artificially,  with  commercial  success. 


As  to  "Harvard"  Brick 

265.  Michigan — Can  you  give  us  any  information  as  to  the 
name  and  location  of  the  manufacturers  of  the  "Harvard" 
brick  ? 

Genuine  "Harvard"  brick  are  made  only  in  New  England 
— that  is,  in  New  Hampshire,  Vermont,  Massachusetts  and 
Connecticut.  The  greater  proportion  of  the  output  is  con- 
trolled by  the  New  England  Brick  Company,  with  offices  at 
178  Devonshire  St.,  Boston,  Mass.  Parry  Brothers,  of  166 
Devonshire  St.,  Boston,  Mass.,  have  yards  at  Epping  and  at 
Gonic,  N.  H.,  where  they  make  one  of  the  best  "Harvards" 
on  the  market.  The  Spiers-Fish  Brick  Company,  of  79  Milk 
St.,  and  D.  Washburn  &  Sons,  of  166  Devonshire  St.,  Bo3- 


CLAYWORKING  PROBLEMS  101 

ton,  Mass.,  are  also  producers — the  latter  making  the  famous 
"Washburn"  Harvard  brick,  of  which  are  specified,  probably, 
ten  times  the  number,  each  year,  as  the  Washburn  yards  can 
produce.  No  "Harvards"  that  is,  no  brick  that  resembles 
the  "Harvard,"  even  distantly,  is  made  anywhere  outside  of 
New  England.  Genuine  "Harvards"  are  made  of  a  peculiar 
clay,  are  hand-molded  and  water  struck.  They  have  a  cer- 
tain proportion  of  the  headers  ranging  in  shade  from  dark 
red  to  green — the  latter  shade  being  produced  by  burning 
with  wood.  The  heads  are  wrinkled  and  cracked,  and  never 
have  been  successfully  imitated  in  any  way  other  than  the 
New  England  method  of  burning,  nor  in  any  clay  other  than 
that  found  in  the  New  England  states. 


Wants  Formulae  for  Coloring  Mortar 

457.  Quebec — Will  you  please  answer  the  following  ques- 
tion in  the  next  issue  of  "Brick  and  Clay  Record" — What  is 
the  best  composition  for  coloring  lime  and  cement  mortar? 

The  greatest  difficulty  in  securing  stable  colors  for  lime 
and  cement  mortars  is  due  to  the  action  of  lime  on  many 
colorants.  The  most  satisfactory  pigments  are  the  metallic 
oxides.  Hematite  or  Fe2Oj  is  most  commonly  employed  for 
the  red  colors,  while  the  brown  oxide  of  iron  is  used  for 
buffs  and  browns.  Yellows  are  obtained  by  use  of  ochre. 
The  best  greens  are  obtained  by  the  use  of  chromium  oxide, 
but  this  of  course  is  very  expensive.  Ultramarine  green  is 
very  satisfactory  as  far  as  color  is  concerned,  but  it  is  grad- 
ually destroyed  by  lime.  Lamp  black  is  most  commonly  em- 
ployed as  a  pigment  in  the  production  of  black. 


Brick  Made  From  Blast  Furnace  Slag 

491.  Ohio — Have  you  any  information  as  to  the  manu- 
facture of  brick  in  this  country  from  blast  furnace  slag? 
Do  you  know  of  any  plants  in  this  country  that  are  using  this 


102  CLAYWORKING  PROBLEMS 

material  for  manufacturing  brick?  As  we  understand  the 
process,  it  is  similar  to  that  of  manufacturing  sand-lime  brick. 
We  would  also  like  to  have  the  names  of  the  manufacturers. 
Any  information  you  can  give  us  will  be  appreciated. 

Several  attempts  have  been  made  to  manufacture  brick 
from  blast  furnace  slag,  a  plant  having  been  built  in  Mil- 
waukee, and  one  at  Youngstown,  Ohio — the  latter  for  the 
Brier  Iron  and  Coal  Company.  The  processes  were  used,  one 
of  them  being  to  crush  the  cold  clinker  and  mix  with  a  bond- 
ing member  after  which  they  were  pressed  into  brick — the 
other  consisting  of  the  immersion  of  the  hot  clinker  in  water 
and  grinding  the  resultant  globule  of  slag.  Difficulties  in 
manufacture  were  experienced  in  both  methods  and  the  varia- 
tion in  the  color  of  the  burned  product  was  such  as  to  make 
the  plants  mentioned  unprofitable.  We  believe  that  every 
plant  that  has  so  far  been  started  in  this  country  for  the  pur- 
pose of  making  brick  from  blast  furnace  slag  has  been  closed 
down. 


Roofing  Tile  Manufacture 

H9G.  Kentucky — 17 V  would  like  to  have  some  information 
on  the  status  of  the  roofing  tile  business  in  this  country,  es- 
pecially in  Kentucky.  Is  there  a  good  demand  for  roofing 
tile?  It  seems  that  we  are  unfortunately  located  for  a  drain 
tile  plant  and  we  arc  wondering  if  we  could  not  use  our 
round-down-draft  kilns  and  drain  tile  machinery  profitably 
in  the  production  of  roofing  tile  provided  our  clay  is  suit- 
able. We  understand  that  we  would  have  to  add  some  more 
machinery. 

The  manufacture  of  roofing  tile  in  this  country  is  yet  in  its 
infancy.  There  are  only  a  few  plants,  and  until  recently  most 
of  the  tile  used  was  imported.  There  is  a  good  demand  for 
the  product  and  the  few  plants  that  are  making  it  ship  ex- 
tensively. Most  of  these  plants  are  located  in  and  around 
the  larger  cities,  particularly  in  Indiana  and  Ohio.  The  man- 


CLAYWORKING  PROBLEMS  103 

ufacture  of  roofing  tile  offers  many  difficulties.  A  clay  that 
may  make  a  good  drain  tile  may  not  make  roofing  tile. 
Your  material,  therefore,  should  not  only  be  thoroughly  tested 
as  to  its  physical  and  pyrochemical  behavior,  but  the  extent 
and  uniformity  of  character  of  the  deposit  should  also  be 
studied  carefully. 

There  are  two  kinds  of  tile  made — porous  and  vitrified. 
What  style  you  make  depends  upon  the  kind  of  clay  you  have. 
In  the  manufacture  of  the  porous  tile  the  manufacturer  should 
make  his  tile  before  it  goes  to  the  kiln,  while  the  vitrified 
manufacturer  depends  upon  the  burning  to  make  his.  In  other 
words  the  porous  tile  should  receive  much  the  greater  atten- 
tion in  the  preparation  of  its  raw  material  and  in  the  form- 
ing, for,  if  the  tile  is  not  strong  and  solid  when  dried,  it  will 
scarcely  harden  and  strengthen  enough  in  the  firing  process 
to  make  it  frost-proof. 

The  vitrified  tile  may  be  made  from  granular,  poorly  pre- 
pared raw  material  but  if  it  is  of  the  right  vitrifying  quali- 
ties it  may  be  made  durable  by  hard-burning. 

The  porous  tile  manufacturer  has  much  the  best  of  the 
argument.  By  using  extreme  care  in  handling  his  crude  ma- 
terial, the  working  of  which  can  be  largely  handled  by  ma- 
chinery, he  obtains  a  product  that  goes  into  the  kiln  in  the 
best  condition — that  is  sound  and  straight.  By  stopping  the 
burning  at  a  point  where  the  physical  strength,  though  not  at 
its  best,  is  sufficient,  he  obtains  a  product  that  has  not  under- 
gone any  severe  volume  changes  and,  therefore,  remains 
sound  and  straight,  but  not  brittle. 

One  of  the  greatest  sources  of  loss  in  tile  manufacture  is 
the  warping,  cracking  or  denting  of  the  ware.  The  porous 
tile  maker  has  the  minimum  of  this. 

The  manufacturer  of  the  vitrified  tile  is  apt  to  have  all 
sorts  of  trouble.  To  minimize  this  he  must  use  some  sort 
of  saggers  in  his  burning  to  support  the  tile  on  account  of 
the  great  shrinkage  and  the  tendency  to  warp.  This  means, 


104  CLAYWORKING  PROBLEMS 

of  course,  extra  expense  and  a  large  amount  of  extra  heat 
is  necessary  to  heat  up  this  dead  material  each  time. 

To  first  ascertain  whether  your  clay  is  adaptable  to  the 
manufacture  of  roofing  tile  send  a  sample — at  least  fifteen 
hundred  pounds — to  some  expert  clay  analyst.  Any  of  the 
ceramic  departments  of  the  state  universities,  or  even  the 
machinery  men,  can  tell  you  as  to  what  this  charge  will  be. 

This  analysis  is  necessary  as  it  may  save  you  several  thou- 
sand dollars  in  experiments  later. 

In  the  meantime,  write  to  J.  A.  Bownocker,  state  geologist 
of  Ohio,  at  Columbus,  Ohio,  and  ask  him  to  send  you  Bulletin 
No.  11,  the  price  of  which  is  75  cents.  This  book  is  cloth 
bound  and  contains  nearly  500  pages  of  exclusive  matter  on 
the  subject  of  tile  manufacture,  and  is  the  latest  word  on 
this  subject.  It  was  written  by  Wolsey  Garnet  Worcester, 
with  Prof.  Edward  Orton,  Jr.,  as  collaborator  and  editor, 
and  is  the  most  comprehensive  treatise  on  any  subject  of  a 
similar  nature  we  have  found  printed  in  the  English  language. 

Silica  Sand  Won't  Make  Silica  Brick 

490.  Georgia — In  your  May  19  issue  you  have  an  article 
on  "Refractory  Brick"  by  T.  E.  Montgomery  of  Alfred,  N.  Y. 
In  it  he  states  that  a  sand  or  clay  that  has  97  per  cent  of 
silica  and  3  per  cent  of  impurities  gives  the  best  results. 
Now  we  have  a  bank  sand  that  analyzes  as  follows:  Silica 
(SiO-,)  97.62;  Ferric  Oxide  (Fc2O3)  .71;  Titanium  Dioxide 
(TiOx)  .09;  Undetermined,  1.36;  Loss  on  Ignition,  .22.  We 
would  like  to  find  out  if  a  good  silica  fire  brick  could  be  made 
from  this  sand  and  if  there  is  any  literature  that  covers  the 
subject.  We  know  that  there  are  numbers  of  silica  fire  brick 
being  made,  but  arc  absolutely  in  the  dark  as  to  where,  or 
hoiv.  Can  you  either  give  us  the  information  or  put  us  in 
touch  with  some  one  who  is  competent  and  reliable?  Any 
assistance  you  may  render  us  will  be  greatly  appreciated. 

The  manufacture  of  silica  brick  from  silica  sand  has  been 


CLAYWORKIXG  PROBLEMS  105 

tried,  but  almost  invariably  with  unsatisfactory  results.  In 
order  that  the  brick  may  have  the  proper  porosity,  it  is  neces- 
sary to  grind  a  material  that  will  make  a  product  coarser 
than  sand,  and  that  will  give  particles  irregular  in  size  and 
shape.  The  process  of  making  silica  brick  includes  the  crush- 
ing of  gannister  rock  in  very  heavy  crushers,  then  putting  the 
ground  material  through  wet  pans,  where  it  is  mixed  with 
the  bonding  material,  and  from  these  pans  it  is  molded  in 
brick. 


Manganese  in  Connection  with  Shale 

456  Quebec — Can  you  tell  us  to  what  degree  shale  brick 
should  be  burned,  to  fuse  manganese? 

Charles  F.  Binns,  director  of  the  New  York  State  School 
of  Clayworking  and  Ceramics,  at  Alfred,  N.  Y.,  says: 

"Manganese  is  used  to  darken  the  color  of  the  brick  or 
tile  which  may  be  made  from  a  red  burning  clay  or  shale, 
but  its  principal  use  is  in  the  production  of  gray  brick  from 
a  light  burning  clay.  It  is  generally  considered  that  in  order 
to  produce  an  effective  gray  brick,  the  temperature  should  be 
at  approximately  Cone  6,  because  at  a  lower  temperature  the 
manganese  grains  appear  as  tiny  specks,  and  do  not  produce 
a  general  gray  tone.  This  temperature,  however,  is  far 
higher  than  anything  generally  used  for  sales.  In  fact,  the 
use  of  the  manganese  must  give  way  to  the  burning  tem- 
perature of  the  shale  and  whenever  vitrification  is  approached 
or  reached,  the  brown  color  will  be  evident  when  manganese 
is  used." 

Charles  S.  Kinnison,  of  the  Bureau  of  Standards  at  Pitts- 
burgh, Pa.,  says: 

"Manganese  is  never  used  in  connection  with  shale  in  the 
manufacture  of  brick.  Manganese  finds  use  only  in  brick 
burning  to  a  clean  light  color  and  it  is  absolutely  essential 
that  the  fire  be  strictly  oxidizing  in  order  fo  develop  in  the 


106  CLAYWORKING  PROBLEMS 


brick  a  clean  light  color  to  act  as  a  background  for  the 
black  manganese  specks.  The  clay  most  commonly  used  in 
connection  with  manganese  is  a  No.  2  or  3  fire  clay.  The 
temperature  needed  for  the  development  of  the  black  specks 
is  cone  2  to  3." 

Ellis  Lovejoy,  E.  M.,  of  Columbus,  Ohio,  writes: 

"In  regard  to  the  temperature  to  which  shale  brick  should 
be  burned  to  fuse  manganese,  we  do  not  know.  There  is 
really  no  relation  between  the  melting  point  of  manganese 
dioxide  and  its  fusion  in  connection  with  other  minerals. 

"In  products  made  of  plastic  fire  clay,  it  is  our  experience 
that  the  manganese  begins  to  combine  with  the  silica  and 
other  minerals  in  the  clay  at  a  temperature  of  about  Cone 
3  (2174°  F.)  and  the  most  satisfactory  results  were  ob- 
tained above  this  temperature,  up  to  about  Cone  7  (2318° 
F.).  In  red  burning  shale,  which  matured  at  kiln  tempera- 
tures below  Cone  1,  we  found  very  little  fusion,  in  fact,  so 
little  that  the  color  effect  of  the  manganese  on  the  ware 
was  practically  nil. 

It  may  be  that  other  shales  would  develop  color  from 
the  manganese  at  lower  temperatures  than  in  our  experi- 
ence, provided  the  shale  vitrified  at  lower  temperatures. 

We  do  not  believe  that  anyone  can  pre-determine  at  what 
temperature  the  manganese  will  become  effective. 

Minerals  which  melt  at  high  temperatures  combine  with 
other  minerals  into  a  fused  mass  at  much  lower  tempera- 
tures. As  an  illustration,  we  use  lime  as  a  flux  in  the  blast 
furnace,  but  lime  itself  is  infusible  at  blast  furnace  tem- 
peratures. The  elements  to  be  fluxed  are  silica  and  alum- 
ina in  the  ore  and  coke,  together  with  some  alkalies  and 
alkaline  earth.  Silica  itself  is  infusible  at  blast  furnace 
temperatures,  and  so  also  is  alumina.  Here,  then,  we  have 
three  practically  infusible  minerals,  which  in  combination 


CLAYWORKING  PROBLEMS 107 

form  a  slag  which  becomes  quite  liquid  at  blast  furnace  tem- 
peratures. 

In  a  clay  mass  we  have  silica,  alumina,  lime,  magnesia, 
iron  and  alkalies.  Except  the  alkalies,  all  of  these  min- 
erals, individually,  are  infusible  at  kiln  temperatures,  and 
yet,  we  combine  them  very  readily  at  kiln  temperatures  into 
vitrified  bodies.  All  clays  contain  the  above  minerals  in  vary- 
ing proportions,  but  the  temperatures  at  which  they  began 
to  vitrify  are  widely  different,  due  to  the  variation  in  quan- 
tity of  the  several  minerals. 

We  describe  the  fusion  as  rock  solution.  The  alkalies  or 
alkali  containing  minerals,  such  as  feldspar,  will  melt  at  rela- 
tive low  temperatures  and  as  they  begin  to  melt  they  take  up 
(dissolve)  silica  and  alumina  together  with  the  other  minerals 
present  in  increasing  degree  as  the  temperature  advances  and 
as  the  alkali  solution  tends  to  become  fluid.  This  tendency 
to  fluidity  is  offset  by  the  increased  quantity  of  silica  and 
alumina  taken  up  and  in  this  way  the  vitrification  advances 
from  a  very  insipient  stage  to  a  completely  vitrified  or  fused 
mass,  in  which  the  rock  solution  is  complete. 

In  some  clays  the  fusion  starts  at  a  very  low  tempera- 
ture and  in  such  clays  we  would  expect  a  solution  of  man- 
ganese into  the  fused  mass  along  with  the  other  minerals 
present,  and  in  such  event  we  would  get  color  effect  from 
the  manganese. 

Clays  requiring  higher  temperatures  to  vitrify,  therefore, 
will  involve  such  higher  temperatures  to  get  the  manganese 
into  solution  and  from  it  thereby  its  color  effect. 

We  get  fusion  of  the  manganese  and  the  color  effect  there- 
from in  many  products  in  which  there  is  no  evidence  of  fusion 
except  in  the  manganese  spots  and  in  our  experience  this  only 
occurs  at  temperatures  above  Cone  3. 

In  such  instances  the  manganese  becomes  the  fluxing  ele- 
ment and  takes  up  silica,  etc.,  to  form  a  rock  solution,  where 
at  lower  temperatures  some  mineral  which  fused  at  such  low- 


108  CLAYWORKING  PROBLEMS 

er  temperatures  is  the  fluxing  mineral  and  the  manganese  is 
simply  one  of  the  minerals  dissolved  in  the  fused  mass. 

Manganese  was  formerly  largely  used  in  connection  with 
red  burning  clays  to  produce  a  brown  brick,  but  at  the  pres- 
ent time  there  is  very  little  demand  for  this  color  as  produced 
from  manganese,  since  we  are  able  to  produce  various  shades 
of  co!or  from  red,  through  brown,  to  gun-metal  black  by  fire 
flashing  the  red  burning  clay,  and  these  colors  are  more 
effective  than  the  manganese  browns  formerly  produced." 


Substituting  Chimney  for  Fan  Draft 

517.  North  Carolina — We  are  operating  a  continuous  kiln 
of  the  tunnel  type  and  obtain  a  satisfactory  draft  by  using  an 
American  Blower  Company's  No.  70  fan  driven  by  a  seven 
and  one-half  horsepower  motor.  We  have  occasionally,  how- 
ever, experienced  some  trouble  on  account  of  the  irregular- 
ity of  our  power  supply,  finding  it  next  to  impossible  to  keep 
our  engine,  generator  and  motor  running  continuously.  Will 
you  kindly  advise  us  what  size  and  height  stack  it  zvould  take 
to  give  us  tlie  same  results  as  we  obtain  with  the  fan  when 
we  are  able  to  keep  it  running!' 

To  begin  with,  without  trying  to  avoid  a  direct  answer 
to  your  question,  fan  draft  on  a  continuous  kiln  is  much  bet- 
ter than  stack  draft  because  of  its  uniformity  and  perfect 
control.  Nearly  all  continuous  kilns  now  being  built  have 
fan  draft,  which  enables  the  operator  to  burn  much  more 
quickly  than  with  the  weaker,  irregular  stack  draft. 

It  is  not  possible  for  us  to  determine  the  size  and  height 
of  a  stack  suitable  for  your  kiln  without  more  data.  The 
size  of  the  fan  is  given  and  the  power  of  the  motor,  but 
this  is  not  sufficient  to  determine  the  size  of  the  flues  nor 
the  size  of  a  stack  which  will  serve  your  purpose.  If  the 
speed  of  the  fan  had  been  given,  we  could  determine  the 
volume  of  air  which  the  fan  would  deliver  without  any  resist- 


CLAYWORKING  PROBLEMS  109 

ance,  but  even  then  we  could  not  estimate  the  resistance  which 
greatly  reduces  the  volume  of  air.  To  determine  the  proper 
size  of  a  stack,  it  is  necessary  to  have  full  information  in  re- 
gard to  the  size  of  the  kiln,  the  rapidity  of  the  burning,  the 
quantity  of  fuel,  or  in  lieu  of  the  latter,  the  volume  of  gas 
to  be  carried  off  by  the  stack. 

A  German  engineer  gives  the  following  rule  of  thumb  for 
continuous  kiln  stacks,  namely :  the  height  of  the  stack  should 
be  0.5  to  0.6  of  the  length  of  the  tunnel ;  and  we  would  add 
to  this  that  in  no  case  should  the  stack  be  less  than  one  hun- 
dred and  twenty-five  feet  in  height.  The  area  of  the  stack 
should  be  0.16  to  0.17  of  the  cross  section  of  the  tunnel. 

If  your  kiln  has  been  designed  for  fan  draft,  it  is  possible 
that  the  main  flues  are  smaller  than  they  should  be  for  a 
stack. 


Questions  Accuracy  of  Answer  to  Draft  Problem 

589.  New  York— In  the  October  6  issue  of  "Brick  and 
Clay  Record,"  answer  to  question  517,  I'M  the  next  to  last 
paragraph  you  make  a  statement  that  where  a  stack  is  used 
instead  of  a  mechanical  draft  "that  in  no  case  should  the 
stack  be  less  than  one  hundred  and  twenty-five  feet  in  height." 
You  must  have  some  special  reason  for  making  this  state- 
ment, as  ordinarily  the  height  of  chimney  required  depends 
directly  upon  certain  data  which  is  easily  figured.  Under  cer- 
tain conditions,  the  rate  of  combustion  in  a  kiln  is  slow,  com- 
pared to  that  in  a  boiler  fire  box,  but  usually  it  is  more 
favorable  for  producing  high  temperatures.  Naturally  also, 
the  temperature  of  the  gases  being  discharged  from  a  kiln  is 
very  high  as  compared  with  those  coming  from  an  ordinary 
boiler.  A  chimney  fifty  feet  in  height  and  connected  zrith  a 
boiler,  discharging  gases  having  a  temperature  of  five  hundred 
and  fifty-tzvo  degrees  Fahr.,  has  a  draft  power  of  0.365  inches 
of  water  and  should  burn  one  hundred  and  five  pounds  of 
coal  per  hour  per  square  foot  of  chimney  section.  Figuring 


110  CLAYWORKING  PROBLEMS 

roughly,  a  fifty-foot  chimney  two  feet  in  diameter,  inside 
measurement,  should  burn  3.14  times  one  hundred  and  five 
pounds,  or  three  hundred  and  twenty-nine  pounds  of  coal  per 
hour.  Any  chimney  taking  waste  heat  from  a  kiln,  owing  to 
its  high  temperature,  should  be  able  to  do  more  work  than 
the  above  as  its  draft  should  be  greater  than  0.365  inches  of 
water.  Your  statement  that  a  kiln  chimney  should  not  be 
less  than  one  hundred  and  twenty-five  feet  is,  therefore,  in- 
teresting and  the  writer  would  be  very  grateful  for  a  state- 
ment of  your  basis  for  same. 

Our  statement  that  in  no  case  should  the  stack  be  less  than 
one  hundred  and  twenty-five  feet  in  height  is  based  on  prac- 
tical experience  and  not  upon  theoretical  data.  It  is  im- 
possible to  figure  the  proper  height  of  a  stack  for  a  con- 
tinuous kiln.  The  formulae  given  in  various  engineering 
works  on  the  subject  of  stack  draft  apply  particularly  to 
boiler  stacks,  the  problem  having  been  thoroughly  investi- 
gated for  such  work.  A  continuous  kiln  stack,  however,  is 
an  entirely  different  problem. 

The  efficiency  of  a  stack  depends  upon  its  height,  the  tem- 
perature of  the  gases  being  discharged  and  upon  the  re- 
sistance offered  to  the  draft.  The  gases  from  the  kiln  must 
pass  numerous  turns  and  through  a  series  of  closely  set 
checker-work  made  by  the  ware  set  in  the  kiln.  The  dis- 
tance of  this  checker-work  may  be  fifty  or  more  feet  and  it 
is,  therefore,  impossible  to  figure  the  resistance  to  move- 
ment of  the  gases  which  must  be  overcome  by  the  stack. 

Our  correspondent  is  discussing  a  boiler  stack  and  the 
data  he  uses  is  not  applicable  to  a  continuous  kiln  stack. 
The  temperature  of  552  degrees  Fahr.  is  the  maximum  effi- 
ciency temperature,  and  for  that  reason,  it  is  the  temperature 
which  appears  most  generally  in  formulae  for  stacks. 

His  statement  that  "any  chimney  taking  waste  heat  from 
kilns,  owing  to  their  high  temperature,  should  be  able  to  do 
more  work  than  the  above,  etc.,"  is  not  correct.  Any  tem- 
perature above  552  degrees  Fahr.  reduces  the  efficiency  of 


CLAYWORKING  PROBLEMS  111 

the  stack,  and  likewise  any  temperature  below  this  maxi- 
mum efficiency  temperature. 

We  need  not  consider  temperatures  above  this  critical  tem- 
perature, as,  in  a  great  majority  of  cases,  waste  heat  gases 
run  less  than  500,  and  frequently  as  low  as  200  degrees. 
Part  of  the  economy  in  the  operation  of  continuous 
kilns  is  in  using  the  heat  of  the  waste  gases  to  heat  up 
and  watersmoke  the  brick  ahead  of  the  combustion  chambers, 
and  the  gases  are  only  drawn  off  into  the  stack  when  they 
become  ladened  with  moisture  to  approximately  the  dew 
point.  This  is  the  limit  of  the  use  of  the  products  of  com- 
bustion in  a  continuous  kiln,  and  when  this  limit  is  reached, 
the  temperature  of  the  gases  has  fallen  very  much. 

In  a  continuous  kiln  stack  another  factor  enters  which  does 
not  appear  to  any  great  degree  in  boiler  stacks,  namely,  the 
effect  of  the  vapor  which  accompanies  the  kiln  gases.  In 
a  boiler  stack,  as  the  gases  rise,  they  are  cooled  and  the 
efficiency  of  the  stack  varies  accordingly.  In  a  continuous 
kiln  stack,  starting  with  a  temperature  at  least  not  greatly 
exceeding  the  boiling  point  and  with  a  gas  loaded  to  the 
dew  point  with  water  vapor,  as  the  gases  cool  in  their  ascent 
in  the  stack,  condensation  takes  place  and  the  latent  heat 
of  condensation  is  given  up  to  maintain  the  temperature  of 
the  gases,  even  to  the  top  of  the  stack.  Also,  water  vapor 
is  lighter  than  air,  which  increases  the  difference  in  weight 
of  external  and  internal  columns  of  air  and  gas  upon  which 
stack  formulae  are  based.  Furthermore,  continuous  kilns 
use  an  excess  of  air  and  the  CO*  content  in  the  gas  may  be 
even  less  than  five  per  cent,  while  boiler  stack  gases  will 
contain  from  ten  to  fifteen  per  cent.  The  percentage  of  this 
heavy  gas  materially  affects  the  balance  which  causes  the 
movement  of  the  gas  in  the  stack.  The  net  balance  in  weights 
of  air,  water  vapor  and  combustion  gases,  is  indeterminate. 

We  made  no  attempt  to  figure  the  proper  height  of  a  stack 
for  a  continuous  kiln  and  frankly  say  that  the  problem  is 
beyond  our  ability.  In  such  work  we  figure  the  problem  as 


112  CLAYWORKING  PROBLEMS 

far  as  possible  in  order  to  get  some  information  upon  which 
to  exercise  our  judgment,  but  in  exercising  this  judgment, 
we  are  governed  more  by  practical  experience  than  the  re- 
sults of  our  theoretical  estimates. 

In  conclusion  we  may  add  that  stacks  for  continuous  kilns 
are  becoming  a  thing  of  the  past.  With  the  low  temperature 
which  prevails  in  the  stack  sufficient  draft  cannot  be  obtained 
for  the  rapid  operation  of  present  types  of  kilns  and,  in 
consequence,  the  kiln  stacks  are  being  replaced  by  fans  which 
give  a  perfect  control  of  the  draft  and  which  may  be  varied 
to  suit  the  requirements.  The  draft  power  applied  to  con- 
tinuous kiln  suction  exceeds  one  inch  of  water  and  it  would 
be  difficult  to  get  this  power  from  a  stack  construction. 


Proportionate    Kiln    and    Stack    Area 

103.  Missouri — /  noticed  a  question  in  your  February  issue 
regarding  the  proportion  of  stack  area  to  kiln  area.  Did  any 
one  answer  this  question  f  If  so,  will  you  put  me  in  posses- 
sion of  the  information  f 

The  correct  area  of  the  stack,  as  compared  to  the  area 
of  the  kiln,  is  somewha't  over  one-third  stack  area  (figured 
in  cu.  ft.)  to  the  kiln  area  (figured  in  sq.  ft.),  as,  for 
instance,  in  a  kiln  30  ft.  in  diameter,  we  have  an  area 
of  732.62  sq.  ft.,  one-third  of  which  is,  approximately,  243.  It 
is  well  to  increase  this  number,  and,  going  to  a  stack  3x3 
ft.  in  'the  clear  and  40  ft.  high,  we  have  a  draft  area  of 
360  cu.  ft.  A  stack  of  these  dimensions  is  larger  than 
needed  at  the  finish,  but  is  needed  in  watersmoking  and 
oxidation. 


Bricks  Check  After  Pressing 

53.  Alberta — We  have  a  Berg  dry  press  and  manufacture 
high-grade  face  brick,  but  arc  having  trouble  with  checking 
of  brick  before  they  arc  burned.  We  would  like  to  overcome 
this,  as  it  makes  No.  2  brick  out  of  a  lot  of  otherwise  No.  1. 


CLAYWORKING  PROBLEMS 113 

We  haz'e  an  overburden  of  thirty  feet,  so  we  mine  our  shale 
and,  working  it  direct  from  the  mine,  have  little  chance  to 
weather  it.  We  find  the  brick  check  less  when  the  clay  is  run 
damp  and  think  it  would  be  better  if  the  clay  were  ground  a 
little  coarser.  We  are  using  a  piano-uire  screen,  No.  24  wire, 
nine  wires  to  the  inch,  and  we  do  not  want  to  run  the  clay 
coarser,  as  it  would  not  give  us  as  smooth  a  brick  nor  such 
li'dl  defined  edges. 

The  trouble  probably  lies  in  the  air  holes  in  the  top  of  your 
press  being  clogged  up  or  in  your  running  too  fast.  In  either 
case,  the  air  that  is  mixed  with  the  clay  when  it  enters  the 
press  has  too  little  chance  to  escape  in  pressing  and,  as  a 
consequence,  compresses  with  the  clay.  It  expands  after  the 
bricks  leave  the  press,  seeking  an  outlet  through  the  face  of 
the  brick,  checking  them  as  it  makes  its  exit.  Having  looked 
at  the  air  holes,  try  running  your  press  a  little  slower  and 
note  the  result 

After  the  above  had  been  published,  the  correspondent  who 
asked  the  question  wrote  another  letter,  in  which  he  said : 

"Some  time  ago  I  wrote  you  in  regard  to  our  brick  check- 
ing, and  you  recommended  that  we  examine  the  air  holes  on 
the  press  and  see  that  we  were  not  running  too  fast.  All 
this  lie  had  previously  done,  so  we  did  not  gain  very  much 
information  from  your  reply,  which,  by  the  way,  I  see  the 
'Canadian  CIa\  Worker1  for  June  has  copied.  However,  we 
thank  you  for  your  reply,  and  would  say  that  we  overcame 
the  difficulty  in  another  way. 

"We  built  wings  to  our  shale  trestle,  to  the  right  and  left, 
14  //.  high  and  100  ft.  long.  While  we  were  using  up  one  side 
we  filled  up  the  other  uith  shale,  and  also  ran  a  ^-inch  stream 
of  water  on  each  day's  mining  for  three  hours.  This  water 
and  the  wind  and  sun  has  a  wonderful  effect  on  our  shale  in 
the  two  weeks  7ir  can  allow  it  to  weather.  We  also  mix  a 


CLAYWORKING  PROBLEMS 


little  grog  in  the  shape  of  brick  bats,  and  the  checking  is  en- 
tirely done  away  with. 

"We  arc  burning  SO  per  cent  No.  1  face,  10  per  cent  No.  2 
and  10  per  cent  common,  at  prices  ranging  from  $9.50  per  M. 
for  commons  to  $15.00  and  $40,00  per  M.  for  face  brick.  Our 
shale  is  very  rich,  fat  and  plastic,  and  we  manufacture  511,000 
per  month. 

"Hoping  this  ict'//  help  some  fellow  out  of  his  troubles,  as 
I   lost  some  sleep   over  it   the  first  month  I  ivas   here,  and 
thanking  you  again  for  your  reply,  I  am 
Yours  very  truly, 

,  Supt." 


Dry  Press  Brick  Check 

331.  Texas — IV c  arc  running  a  dry  press  brick  plant,  op- 
erating two  presses,  one  a  Ross-Keller,  triple  pressure  and 
the  other  a  Grath  fire-mould  special.  We  have  been  having 
considerable  trouble  with  our  brick  air-checking  shortly  after 
it  comes  from  the  press  usually  from  one-half  of  an  hour  to 
two  hours  and  this  trouble  has  been  more  noticeable  of  late. 
The  air-checking  does  not  occur  at  all  times  but  is  worse 
when  we  have  a  cold,  dry,  strong  north  wind.  Wind  from 
any  other  quarter  apparently  does  not  check  them  so  much 
and  when  the  air  is  damp  and  foggy,  there  are  no  checks  at 
all.  Our  kilns  are  not  protected  from  the  north  winds.  The 
air  checks  do  not  seem  to  burn  out.  The  clay  burns  a  yellow 
or  buff  color,  which  is  very  pretty  and  if  we  could  only  get 
rid  of  the  checks,  we  would  have  as  fine  a  brick  as  is  manu- 
factured in  this  state.  The  brick  takes  considerable  heat,  re- 
quiring at  least  2,000  degrees.  We  use  two  barrels  of  oil  and 
the  moisture  we  use  is  from  six  to  ten  per  cent. 

The  trouble  you  are  experiencing,  due  to  the  development 
of  air  cracks,  is  a  common  one  to  the  manufacturer  of  dry 
pressed  brick,  especially  where  the  material  used  is  prac- 
tically non-plastic.  Two  possible  remedies  suggest  themselves. 


CLAYWORKING  PROBLEMS  115 

One  is  to  store  the  clay  as  long  a  time  as  is  practical  (two 
or  three  days)  before  using  it.  The  clay  must,  of  course, 
be  in  the  moist  condition  when  stored,  just  about  as  it  will 
be  when  used  at  the  press.  If  your  plant  is  small,  you  prob- 
ably will  not  be  able  to  store  it  longer  than  24  hours  but 
even  this  short  a  time  may  help  you  somewhat.  The  second 
suggestion  is,  before  setting  to  put  the  brick  into  a  warm, 
damp  compartment  where  little  drying  will  be  accomplished 
but  yet  where  the  brick  can  be  warmed  up.  When  run  out 
of  this  damp  closet,  the  ware  should  show  a  lessor  tendency 
to  develop  the  air  cracks  of  which  you  speak. 

This  question  was  submitted  to  other  authorities  on  the 
subject,  who  replied  as  follows : 

Anton  Berg,  of  the  Berg  Machinery  Manufacturing  Co., 
Toronto,  makers  of  the  Berg  dry  press,  offers  this  sugges- 
tion :  "In  some  cases  by  having  a  steamer  and  steaming  the 
clay  so  that  it  will  be  warm  and  dry  inside  of  the  brick,  has 
proved  successful,  and  again,  in  some  cases,  weathering  is  a 
remedy  for  air-checking." 

Ellis  Lovejoy  writes:  "As  a  rule  the  finer  ground  the  clay 
is  and,  in  consequence,  the  greater  the  density  of  the  brick, 
the  greater  is  the  checking  difficulty.  There  are  very  few 
dry  press  brick  which  will  not  air-check  when  left  exposed 
to  the  air  or  sun,  particularly  when  the  air  has  very  little  hu- 
midity, or,  in  other  words,  when  it  has  great  drying  capacity. 
It  is  simply  an  illustration  of  the  surface  drying  faster  than 
the  moisture  within  the  brick  can  be  brought  to  the  sur- 
face and  the  surface  drying  causes  shrinkage  on  the  sur- 
face and  the  strains  introduced  by  this  shrinkage  are  coun- 
teracted by  the  numerous  cracks.  When  the  bond  is  once 
broken  by  these  cracks,  it  will  not  knit  together  in  the  burn- 
ing. Many  years  ago  the  manufacturers  of  dry  press  brick 
began  the  introduction  of  dryers  in  order  to  reduce  the 
time  of  drying  in  the  kilns,  but  almost  without  exception 
the  dryers  were  found  to  be  a  failure  simply  because  the 


116  CLAYWORKING  PROBLEMS 

brick  would  check  more  or  less  in  the  dryer,  but  would 
not  check  in  the  kiln  and  in  consequence  the  manufacturers 
returned  to  the  usual  method  of  setting  the  brick  from  the 
machine  direct  into  the  kiln.  The  only  method  we  can  sug- 
gest in  this  instance  is  to  protect  the  brick  from  sun  and 
wind.  This  is  not  always  easy  to  do  in  updraft  kilns  and 
we  have  found  it  necessary  in  using  such  kilns  for  dry  press 
brick  to  follow  the  setting  very  closely  with  the  platting  and 
in  a  scove  kiln  it  would  be  necessary  to  keep  the  scoving  up 
to  the  setting.  If  the  kilns  are  scove  kilns  and  it  is  not 
practical  to  keep  the  scoving  close  to  the  setting,  probably 
dampened  burlaps  hung  over  the  exposed  brick  would  pro- 
tect them  from  the  action  of  the  wind  and  in  the  kiln,  as 
the  setting  progresses,  the  exposed  benches  can  be  similarly 
protected." 

As  to  Care  of  Belting 

249.  Georgia—I  want  some  information  as  to  the  proper 
care  of  belting.  We  use  a  great  deal  of  cotton  stitched  belt. 
We  find  it  preferable  to  rubber  belt,  but  the  belt  gets  stretched 
a  great  deal  when  ive  hare  a  high  wind  and  becomes 
very  hard  and  dry  on  account  of  the  dust  flying  around  the 
brick  yard.  Our  belt  bill  is  enormous.  We  use  entirely  too 
much  belt  and  do  not  get  near  the  life  out  of  the  belt  that 
we  should.  We  would  like  to  have  some  suggestions  in  re- 
gard to  this  and  would  be  glad  if  you  would  give  it  as  much 
publicity  as  you  think  practical.  We  believe  a  discussion 
would  be  valuable  to  all. 

We  have  submitted  this  problem  to  a  number  of  practical 
engineers  and  to  some  of  the  belt  manufacturers.  One  en- 
gineer, who  has  to  contend  with  all  sorts  of  belts  under  all 
sorts  of  conditions,  suggests  the  use  of  castor  oil  on  the  can- 
vas belt  to  keep  it  soft  and  pliable.  All  belts,  especially  if 
exposed  to  the  air  much,  require  a  dressing  of  some  sort  and 
castor  oil  is  far  better  than  most  of  the  advertised  products. 


CLAYWORKING  PROBLEMS  117 

It  does  not  injure  the  fabric  as  does  linseed  oil  and  other 
substances.  A  belt  manufacturer  solves  the  problem  in  this 
manner:  "Some  cotton  stitched  belts  are  filled  with  com- 
pounds which,  while  affording  some  lubrication  for  the  fibres 
of  the  belt  when  first  installed,  soon  oxidize,  and  become 
hard,  causing  internal  wear.  A  high  grade  stitched-canvas 
belt  is  filled  with  a  non-oxidizing  compound  which  maintains 
pliability.  Furthermore,  a  high  grade  belt  of  this  kind,  aside 
from  being  filled  with  a  heavy  compound  which  does  not  get 
hard,  causing  internal  wear  and  the  breakage  of  the  belt,  is 
covered  with  an  outer  coating  of  a  heavy  mineral  compound 
which  hermetically  seals  the  inner  lubrication,  keeping  the  belt 
pliable.  We  have  known  of  instances  where  cheap  belts  did 
not  give  economical  service,  and  the  user  in  looking  for  relief 
used  too  heavy  a  belt,  that  is,  a  belt  of  too  many  plies  for  the 
too  heavy  a  belt,  that  is,  a  belt  of  too  many  plies  for  the 
size  of  his  pulleys.  Care  must  be  exercised  in  selecting  belts 
to  see  that  too  heavy  a  belt  is  not  used  on  small  pulleys, 
as,  regardless  of  the  quality  of  belting,  if  it  is  too  heavy 
for  the  pulleys,  the  belt  will  soon  be  broken  down." 


Adding  Oxide  of  Iron  to  Produce  Red  Color. 

100.  Indiana — IV e  note  in  your  "Questions  and  Answers" 
department  for  April  15  the  following  by  67  Havana:  "What 
can  I  add  to  a  white  clay  in  order  to  obtain  a  red  brick?" 
You  reply  that  the  clay  may  be  burnt  red  by  adding  oxide 
of  iron.  Can  you  give  us  some  successful  method  of  adding 
this  to  the  clay? 

Ellis  Lovejoy,  E.  M.(  of  Columbus,  Ohio,  gives  the  follow- 
ing answer : 

In  reply  to  your  inquiry  relative  to  obtaining  a  red  color 
from  a  buff  burning  clay,  your  answer  "67  Havana"  to  the 
question  is  in  the  main  correct,  except  the  last  statement  in 


118  CLAYWORKING  PROBLEMS 

the  first  paragraph.  This  last  statement,  "Clays  con'taining 
little  alumina  and  much  iron  burn  red,"  is  true  enough,  but 
it  also  may  be  said  that  clays  containing  much  alumina  and 
much  iron  burn  red. 

It  is  the  "much  iron"  that  coun'ts  and  the  content  of  alum- 
ina has  very  little  to  do  with  it.  We  have  found  that  a  high- 
ly aluminous  clay  containing  iron,  of  course,  will  burn  a 
dull  brown  red  while  a  silicious  clay  will  have  a  bright  red 
color,  but  both  are  red. 

Your  correspondent  says,  "the  effectiveness  of  iron  as  a 
coloring  agen't  depends  not  only  upon  the  quantity  used  but 
also  upon  the  degree  of  oxidation  and  upon  the  physical  and 
chemical  condition  of  the  clay,"  to  which  we  agree,  but  we 
would  also  add  that  the  physical  condition  of  the  iron  is 
an  important  factor.  A  clay  containing  five  per  cent  of 
iron  oxide  will  burn  red  provided  i't  is  not  affected  by  the 
"chemical  condition"  of  the  clay.  This  assumes  that  the 
iron  is  in  a  finely  divided  state  and  is  distributed  through  the 
clay. 

Suppose  that  we  have  a  buff  burning  clay  free  from  lime 
and  containing  very  little  iron.  Now  let  us  add  to  i't  a 
lump  of  iron  ore  equal  to  five  per  cent,  or  a  few  nails  equal 
to  five  per  cent  iron  oxide.  The  clay  will  not  burn  red  in 
consequence. 

We  may  divide  the  iron  into  a  dozen,  a  hundred,  a  thou- 
sand pieces  and  still  get  very  little  red  color  from  it.  I't  is 
the  infinitesimal  division  we  get  in  nature  that  gives  us  the 
effective  red  color  of  naturally  red  burning  clays.  We 
cannot  get  this  fine  division  mechanically. 

The  usual  material  added  'to  clays  to  get  a  red  color  is 
finely  divided  hematite  ore,  or  better  the  extremely  finely 
divided  mineral  paint  made  by  roasting  ferrous  sulphate. 

We  have  often  considered  the  possibility  of  coloring  buff 
burning  clays  chemically  and  thus  duplicating  nature's  work. 
If  we  could  add  a  solution  of  iron  to  a  clay  and  then  evapo- 
rate it,  or  decompose  it,  as  the  case  may  be,  we  would  have 


CLAYWORKING  PROBLEMS  119 

each  grain  of  the  clay  coated  with  iron  in  a  finely  divided 
state — an  iron  stain  we  may  say,  we  would  produce  a  red 
burning  material. 

Iron  ores — the  oxides  and  carbonate,  are  not  soluble  and 
consequently  cannot  be  added  in  solution.  We  can  only  add 
them  as  mixtures  and  when  we  add  enough  of  the  oxide, 
let  us  say,  we  will  get  a  dark  brown  red  color  simply  be- 
cause the  color  effect  of  the  iron  predominates  and  hides 
the  buff  color  of  the  clay. 

We  add  manganese  to  a  buff  burning  clay  to  produce  a 
gray  color,  but  it  is  simply  a  pepper  and  salt  gray  and  will 
approach  a  solid  color  with  increasing  degree  of  fineness 
of  the  manganese.  Similarly  with  the  oxide  of  iron. 

We  can  make  a  light  burning  sand  red  by  soading  it  in  a 
solution  of  ferrous  sulphate  then  drying  it  in  the  sand 
dryer  such  as  is  used  in  soft  mud  brick  yards  where  the 
brick  are  sand  molded.  Perhaps  one  soaking  and  drying 
may  be  sufficient,  but  if  not  we  may  get  the  color  to  any 
desired  depth  by  repeating  the  process.  We  consider  this  a 
much  better  method  of  improving  the  color  of  sand  molded 
brick  than  by  the  common  method  of  adding  powdered  iron 
ore. 

Now  the  question  arises,  can  we  do  the  same  with  clay 
and  thereby  color  the  entire  body  of  the  brick? 

We  do  not  know.  The  cheapest  iron  compound  that  is 
soluble  is  copperas — ferrous  sulphate.  This  salt  contains 
20%  iron,  or  26%  ferrous  oxide,  or  29%  ferric  oxide,  as- 
suming that  all  the  oxygen  comes  from  the  salt.  Our  basis 
of  figuring  should  probably  be  on  the  basis  of  26%  ferrous 
oxide  subsequently  oxidized  to  the  red  oxide  in  burning. 

If  one  thousand  brick  requires  6,000  pounds  of  clay  there 
should  be  added  to  it  at  least  (5%)  300  pounds  of  ferVic 
oxide,  or  in  round  numbers,  1,000  pounds  of  ferrous  sulphate 
in  solution. 

To  one  familiar  with  the  behavior  of  sulphur  compounds 
the  objection  will  be  raised  that  in  case  the  clay  contains 


CLAYWORKING  PROBLEMS 


any  lime,  the  sulphur  element  in  the  ferrous  sulphate  will 
combine  with  lime  and  excessive  scumming  will  result.  This 
will  undoubtedly  be  the  case  and  while  we  will  produce  a 
red  color  we  at  the  same  time  bury  it  under  a  dirty  white 
scum. 

Naturally  the  next  s'tep  would  be  to  add  barium  carbonate 
or  barium  hydrate  to  precipitate  the  sulphur  and  in  so  doing 
we  would  at  the  same  time  precipitate  ferric  carbonate  or 
ferric  hydrate  since  either  are  practically  insoluble.  How- 
ever, we  would  accomplish  results  since  the  iron  would 
be  distributed  through  the  clay  in  a  perfect  manner  and  every 
grain  of  clay  would  be  coated  with  a  film  of  the  precipitate, 
or  even  if  coagulation  took  place  every  pore  in  the  clay 
mass  would  be  more  or  less  filled  with  iron  precipitate. 

If  the  clay  did  no't  contain  lime,  probably  the  sulphur  ele- 
ment from  the  decomposition  of  the  ferrous  sulphate  would 
pass  off  without  any  scumming  difficulty  and  in  such  a  case 
we  believe  there  may  be  possibilities  in  treating  a  red  clay 
chemically  to  produce  a  red  colored  brick. 

If,  however,  scumming  results,  the  double  chemical  treat- 
ment, and  the  uncertainty  of  introducing  proper  quantities 
and  getting  complete  reactions,  makes  the  process  a  very 
questionable  commercial  one. 

If  the  clay  is  high  in  lime,  we  have  'the  well  known  com- 
bination of  iron  and  lime  to  form  a  lime  iron  silicate,  with 
the  result  that  the  color  is  a  buff,  greenish  buff,  to  a  green 
regardless  of  the  content  of  iron.  In  such  a  case,  therefore, 
it  would  be  useless  to  try  'to  get  a  red  burning  product. 

Since  sulphur  causes  scumming,  it  might  be  asked  if  there 
is  not  some  other  soluble  of  iron  which  could  be  used. 
We  have  chlorides,  oxalates,  and  nitrates  of  iron  in  both 
the  "ic"  and  "ous"  forms  that  are  soluble,  and  also  the 
bromide,  bu't  the  cost  of  such  chemicals  would  be  prohibitive, 
and  their  effect  need  not  be  discussed. 

In  conclusion  we  have  not  much  confidence  in  the  chemU 
cal  treatment  of  a  buff-burning  clay  to  produce  a  red  color. 


CLAYWORKING  PROBLEMS  13.1 

but  we  believe  that  a  bright  red  burning  sand  for  sand- 
molded  soft  mud  brick  can  be  produced  in  this  way  and 
with  much  more  satisfactory  results  than  the  present  method 
of  adding  powdered  iron  ore.  The  addition  of  iron  ore,  or 
better  the  mineral  pigment,  is  the  most  practical  method  of 
getting  a  red  color  into  a  mass  of  buff-burning  clay,  or,  as 
suggested  by  your  former  correspondent,  by  the  addition  of 
red-burning  clay  or  sand  to  the  buff-burning  material. 


Discolored  Heads  on  Gray  Dry-Pressed  Brick 

671.  Texas — We  manufacture  a  dry-pressed  gray  brick 
made  of  fire-clay  with  manganese  in  it,  and  burn  it  in  round 
down-draft  kilns,  the  brick  being  set  five-over-two.  We  wa- 
ter-smoke with  wood  and  finish  with  oil.  We  hare  trouble 
in  getting  the  heads  of  the  brick  the  same  color  as  the  face, 
the  heads  being  appreciably  darker. 

We  have  calculated  the  amount  of  water  in  the  green  brick 
to  be  one-and-a-half  pounds.  This  conclusion  was  reached 
by  zvcighing  a  brick  that  had  been  burned,  and  comparing  this 
weight  with  the  zveight  of  a  green  brick. 

The  brick  are  taken  direct  from  the  dry-press  to  the  kiln, 
li'hich  is  set  thirty  high.  It  takes  about  four  days  to  fill  the 
kiln,  when  the  water-smoking  is  begun.  This  takes  eight  days; 
we  then  burn  off  with  oil,  which  takes  four  to  five  days  more. 

In  cooling,  we  cut  off  the  burners  and  let  the  eyes  stand 
about  thirty  minutes;  in  the  meantime,  we  take  the  brick  off 
the  center  hole  and  off  the  holes  down  near  the  base  of  the 
crown,  and  drop  the  damper  in  the  main  tunnel  leading  to  the 
stack. 

After  about  thirty  minutes  has  elapsed,  we  daub  the  brick  in 
the  fire-boxes  with  mud.  In  about  twenty-four  hours,  we 
knock  a  small  hole  in  the  brick  in  the  fire-boxes,  and  lift  the 
damper  about  two  or  three  inches.  After  this,  we  gradually 
open  the  fire-boxes  and,  about  the  third  day,  we  begin  to 


122  CLAYWORKING  PROBLEMS 

break  the  door  a  little.  At  the  end  of  seven  days,  the  kiln 
is  cooled  sufficiently  to  work  in. 

We  burn  to  cone  7  (Orton)  sixteen  courses  from  the  top 
and  to  cone  5  two  courses  from  the  bottom. 

We  use  imported  manganese,  which  is  spread  over  the  clay 
at  the  dry-pan  while  the  clay  is  still  in  lumps.  The  manganese 
is  in  powder  form.  We  use  about  fifty  pounds  of  manganese 
per  M.  brick. 

We  are  sending  you  three  samples;  the  piece  marked  1  was 
drawn  from  the  kiln  as  a  trial  piece  while  the  kiln  was  at  a 
high  degree  of  heat,  and  this  sample  appears  to  be  the  same 
color  all  over.  We  did  not  cover  this  piece  up  to  keep  the 
air  from  it,  but  left  it  out,  in  the  open. 

Sample  marked  2,  as  you  will  notice,  is  clouded  on  both 
beds  and  heads,  which  arc  not  at  all  like  the  face  of  the  brick. 
This  is  the  discoloration  that  we  want  to  overcome,  as  we 
want  the  faces,  the  beds  and  the  heads  to  be  alike. 

Sample  marked  3  is  a  part  of  a  brick  that  was  leaked  on 
through  the  kiln,  during  a  rain  that  occurred  while  the  kiln 
was  water-smoking.  You  unit  note  that  where  the  water 
streamed  doivn  upon  it,  the  color  of  the  bed  of  the  brick  is 
the  same  as  the  color  of  the  face.  We  thought  that,  by  send- 
ing you  this  sample  also,  it  might  help  you  to  reach  a  conclu- 
sion as  to  our  trouble. 

But  we  will  also  state,  for  your  information,  that  this  is 
the  third  kiln  that  has  given  us  this  trouble  (the  clouded  ef- 
fect on  beds  and  heads)  and  we  do  not  want  you  to  be  con- 
fused into  thinking  that  it  is  due,  in  any  way,  to  excessive 
rain.  We  want  to  assure  you  that  we  will  appreciate  any  help 
you  can  give  us  in  this  matter,  and  wish  you  the  best  of  suc- 
cess. 

The  discoloration  shown  on  the  samples  submitted  is  a 
scum,  developed  in  the  firing,  but  formed  during  the  drying 
or  water-smoking  period,  or  during  the  interval  immediately 
after  watersmoking. 

Water-smoking  too  fast,  or  two  slowly,  will  develop  scum. 


CLAYWORKING  PROBLEMS  125 

Heating  too  fast  during  this  period  causes  a  rapid  motion  of 
molecules  of  water  toward  the  outside  of  the  brick,  bring- 
ing and  depositing  the  salts  that  are  in  the  clay,  onto  the  sur- 
faces of  the  brick,  as  the  water  evaporates.  It  also  generates 
so  much  steam  that  the  draft  and  flues  are  unable  to  take  care 
of  it.  This  causes  a  surplus  condensation  on  the  exposed  sur- 
faces of  the  brick  and  so  additional  chances  for  concentra- 
tion of  salts  on  those  surfaces. 

When  the  water-smoking  is  too  slow  the  same  results  are 
accomplished.  Steam  is  generated  in  the  top  of  the  kiln  and 
as  no  appreciable  draft  has  been  attained,  the  steam  lingers 
among  the  bottom  brick,  condensing,  and  increasing  the 
chances  for  scumming. 

Incomplete  water-smoking,  followed  by  a  too  rapid  raising 
of  the  heat  results  in  the  quick  expulsion  of  steam,  with  the 
same  results  as  are  noted  above  as  consequent  upon  a  too 
tapid  watersmoking. 

Acting  on  the  assumption  that  your  trouble  is  caused  by 
one  of  the  foregoing  (and  this  assumption  is  strengthened 
by  the  water  content  of  your  green  brick),  we  suggest  that 
you  try  a  remedy  that  was  successful  on  another  plant  which 
made  gray  dry-pressed  brick.  This  was  the  partial  drying 
of  the  brick,  in  the  open  air,  for  forty-eight  hours  before 
the  brick  were  put  into  the  kiln.  The  water-smoking  period 
was  reduced  accordingly,  as  a  much  smaller  amount  of  mois- 
ture was  brought  into  the  kiln  when  the  brick  were  set.  Of 
course,  this  method  has  one  serious  drawback;  with  some 
days  (and  we  know  of  cases  where  this  has  occurred),  air- 
drying  causes  air-slaking,  or  partial  disintegration,  due  to  the 
releasing  of  the  confined  pressure  that  is  given  the  clay  par- 
ticles in  the  press.  The  cohesion  of  the  finely  ground  clay  is 
overcome,  at  times,  by  its  plasticity  and  when  too  great  a 
period  of  time  elapses  between  the  time  of  the  pressure  being 
given  the  clay  in  the  press,  and  the  molecular  changes  that  occur 
during  the  water-smoking  and  burning  periods,  this  cohesion 


124  CLAYWORKING  PROBLEMS 

is   lessened.     This   does   not  occur  to  the  same  extent  with 
every  clay,  and  yours  may,  or  may  not  stand  the  experiment. 

Since  the  above  question  and  answer  was  published  a  letter 
has  been  received  from  R.  H.  West,  of  Alamogordo,  New 
Mex.,  which  gives  another  solution.  His  letter  reads : 

"In  regard  to  the  discoloration  on  your  dry-pressed  brick — 
I  have  handled  southwestern  fire-clays  for  some  years  and 
find  them  very  subject  to  discoloration.  In  your  case,  rather 
than  do  as  you  are  now  doing,  I  should  first  weather  the 
clay  until  it  is  thoroughly  disintegrated  and  take  great  care 
in  the  setting,  trying  benches  of  three  high  and  even  setting 
on  head,  so  that  the  heads  are  kept  close  together  when 
shrunk.  Take  the  usual  precautions  in  watersmoking  and 
raising  heat — I  say  this,  although  I  have  had  very  little 
trouble  in  these  stages,  finding,  rather,  that  the  main  trouble 
with  an  oil  fuel,  comes  in  the  finishing  fires.  I  usually  run 
up  the  fire-box  heat  a  little,  getting  a  perfectly  clear  fire, 
then  drop  my  damper  to  about  four  inches  and  protect  the 
fire-boxes  against  any  wind,  but  do  not  brick  or  daub  them 
up,  and  do  not  remove  any  crown  covers  under  twelve  hours. 
I  find  the  brick  do  not  check  and  the  free  admission  of  air, 
following  a  clearing  fire,  drives  off  the  gases.  I  think  the 
main  fault  is  in  daubing  up  the  finishing  fires."  • 


To  Remove  Scum  or  "Whitewash"  from  Brick  Wall 

676.  Indiana — I  have  mailed  you  today  a  piece  of  our 
brick.  It  is,  as  you  will  see,  whitwashed  in  the  burning. 
What  I  want  to  know  is,  if  there  is  a  solution  of  any  kind 
that  could  be  applied  to  this  brick  after  it  is  built  into  the 
zi'all,  that  zvould  remove  this  scum  and  prevent  its  reappear- 
ing. I  would  also  like  to  know  if  there  is  any  way  to  pre- 
vent this  scum  from  appearing  on  the  brick — that  is,  what  is 
the  best  ivay  to  treat  the  clay  before  or  during  the  pugging, 


CLAYWORKING  PROBLEMS  125 

or  to  regulate  the  watersmoking  or  burning  so  that  the  white 
scum  will  not  appear. 

We  do  not  know  of  any  solution  that  will  remove  scum  or 
efflorescence  from  finished  brickwork.  It  has  been  tried  with 
varying  success,  but  so  far  as  we  have  been  able  to  learn, 
the  relief  has  been  only  temporary  and  the  white  stain  has 
reappeared  after  a  short  time.  If  any  of  our  readers  have 
cause  to  differ  with  us,  we  will  be  glad  to  know  of  their 
experience.  Regarding  the  prevention  of  the  scum  in  the  brick 
itself,  would  suggest  your  reading  Lovejoy's  "Scumming  and 
Efflorescence"  (50c  postpaid)  and  the  many  articles  that  have 
appeared  on  this  subject  in  "Brick  and  Clay  Record." 


Wants  to  Patent  New  Type  of  Kiln 

675.  Tennessee— I  want  to  know  if  there  is  a  down-draft 
kiln  in  use,  ivhich  is  fired  on  one  side,  the  heat  travelling  di- 
rectly across  the  kiln  under  the  floor  and  up  the  bag  walls 
an  the  opposite  side,  with  the  draft  travelling  down,  through 
the  floor,  to  the  stacks.  I  know  of  a  kiln  that  is  something 
similar  to  this,  but  the  stacks  take  the  draft  up  on  the  side  of 
the  kiln,  on  top  of  the  floor.  This  kiln,  however,  has  not 
proved  practical.  I  have  invented  a  kiln  on  the  lines  described 
in  the  first  part  of  this  letter,  and  would  apply  for  a  patent 
upon  it,  if  I  were  sure  that  no  kiln  had  been  built  like  it.  I 
do  not  want  to  infringe  on  anyone's  else  ideas,  and  would  be 
glad  to  know  if  you  know  of  any  similar  kiln  that  is  in  suc- 
cessful operation. 

The  Beaver  Clay  Manufacturing  Company,  of  New  Galilee, 
Pa.,  writes  as  follows : 

"We  have  a  down-draft,  rectangular  kiln  that  we  have  had 
in  use  for  many  years,  and  which  is  fired  on  each  side,  and 
which  had  two  main  side  flues,  and  this  works  on  the  down 
draft  principle.  We  also  have  a  little  test  kiln  which  fires 
from  one  side,  but  the  principle  of  this  test  kiln  we  do  not 


126  CLAYWORKING  PROBLEMS 

consider  as  successful  as  the  principle  of  the  larger  kiln,  which 
is  fired  from  both  sides.  If  your  correspondent  would  care 
to  pay  us  a  visit,  we  would  be  glad  to  show  him  our  kilns, 
for  of  course,  if  his  ideas  are  practically  the  same  as  those 
embodied  in  our  kilns,  it  would  be  useless  for  him  to  secure 
a  patent,  inasmuch  as  the  kilns  have  been  so  long  in  use  that  it 
is  doubtful  whether  a  patent  would  be  issued,  and,  if  it  were 
granted,  whether  it  would  hold." 


Burned  Clay  vs.  Galvanized  Culvert  Pipe 

661.  Georgia — Will  you  tell  us  where  zue  can  get  literature 
to  be  used  in  a  fight  which  we  are  making  against  galvanised 
culvert  pipe? 

We  regret  that  we  are  unable  to  help  you  in  this  matter, 
not  knowing  of  any  printed  matter  on  the  subject  mentioned. 
We  take  this  occasion  to  appeal  to  our  readers  for  help.  If 
any  of  them  have  made  clippings  from  articles  which  could 
be  used  to  further  the  cause  of  burned  clay  against  gal- 
vanized culvert  pipe,  we  would  be  glad  to  learn  the  names 
and  dates  of  publication  of  the  periodicals  which  contained 
these  articles.  We  would  also  like  to  hear  from  our  readers 
who  have  had  any  experience  along  the  line  mentioned  and  to 
receive  letters  or  articles  from  them  which  give  good  reasons 
for  the  advocacy  of  burned  clay  pipe,  particularly  as  opposed 
to  galvanized  iron. 


The  Economy  of  Reburning  Soft  Brick 

664.  Colorado — Knowing  that  you  are  familiar  with  all 
branches  of  the  clayworking  business,  I  take  this  means  of 
finding  out  if  it  is  a  good  plan  to  reset  dry-press  salmon  brick 
in  a  doii'n-draft  kiln  and  so  burn  them  again.  The  brick  I 
refer  to  have  not  been  burned  long  enough  in  an  updraft  kiln, 
and  are  real  light  salmon,  or  you  might  call  them  "dobies."  If 
they  are  reset  in  a  doivn  draft  kiln  and  burned  over,  will  it 
make  good,  hard  red  brick  out  of  them?  And  is  it  cheaper  to 


CLAYWORKING  PROBLEMS  127 

handle  them  in  this  manner  than  it  is  to  make  more  brick? 
We  have  about  200,000  of  these  brick  and  would  like  to  know 
what  we  can  do  with  them. 

Wisdom  would  suggest  experimenting  with  the  salmon 
brick — that  is,  placing  several  hundred  of  them  in  a  kiln  that 
is  being  set  with  new  brick.  Set  the  salmon  brick  in  one  col- 
umn, from  bottom  to  top,  and,  when  the  burn  is  over,  make 
a  careful  observation  of  the  salable  qualities  of  these  re- 
burned  brick.  If  they  are  worth  next  to  nothing,  now — and 
are  worth  more  than  the  cost  of  reburning  them,  when  they 
have  been  reburned,  then  there  is  a  greater  economy  in  re- 
burning,  than  there  is  in  making  new  brick.  Another  point  in 
favor  of  reburning  is  that  200,000  brick  that  cannot  be  sold 
simply  occupies  space  that  ought  to  be  given  to  better  ma- 
terial. 

But  it  is  well  to  experiment,  first.  Otherwise,  the  reburn- 
ing might  give  you  nothing  better  than  what  you  now  have, 
and  the  fuel  and  time  and  kiln  room  would  be  wasted. 


Cement  Joints  in  Clay  Sewer  Pipes 

670.  California—What  reply  can  we  make  to  the  statement 
n'hich  we  have  underscored  in  the  enclosed  advertisement 
relative  to  the  use  of  cement  for  joints  in  sewers  constructed 
of  burned  clay  pipef 

The  underscored  paragraph,  in  the  advertisement  which  our 
correspondent  enclosed,  reads  as  follows : 

And  if  sewage  is  so  dangerous  to  cement,  how  about 
the  cement  joint  that  occurs  every  two  and  a  half  feet  in 
all  clay  pipe  sewers?  It  is  useless  for  them  to  say  that 
the  sewage  does  not  come  in  contact  with  the  cement 
mortar  at  the  joint.  Just  look  in  any  sewer  and  see  for 
yourself. 

Any  sane  person  watching  sewer  construction  will  see  that 
the  joint  which  occurs  every  once  in  so  often  in  clay  pipe 
is  made  up  of  neat  cement  and  is  protected  by  the  burnt  clay 


128  CLAYWORKING  PROBLEMS 

of  'the  pipe  itself;  that  is,  it  is  protected  in  everything 
but  a  very  small  part  of  the  joint.  In  this  it  is  very  much 
like  the  joint  between  brick,  and  in  laying  ordinary  common- 
brick,  a  mortar  joint  that  is  one-quarter-of-an-inch  thick  is 
actually  eight  cubic  inches  in  volume,  where  the  brick  used 
measures  eight  by  four  inches  on  the  bed.  When  the  brick 
and  the  joint  is  exposed  to  fire  or  to  any  other  condition 
which  might  produce  a  chemical  change  in  the  mortar  joint, 
a  surface  which  only  amounts  to  two  square  inches  is  ex- 
posed; that  is,  the  surface  of  the  joint  is  but  one-quarter-of- 
an-inch  thick  by  eight  inches  long  and  it  is  only  the  surface 
which  is  exposed. 

In  the  same  manner,  it  is  only  the  edge  of  the  joint  in  the 
sewer  pipe  that  is  exposed  to  the  chemical  action  of  the  sew- 
age. In  the  making  of  cement  pipe,  neat  cement  is  out  of 
the  question  on  account  of  the  cost  and  the  mixture  which 
is  used  to  make  the  pipe  is  very  different  from  the  mixture 
which  is  used  to  make  the  joints  in  sewers  constructed  of 
burned  clay  pipe. 


Coloring  Matter  in  Molding  Sand 

655.  Pennsylvania — In  a  recent  issue  of  "Brick  and  Clay 
Record"  I  saw  an  article  on  coloring  sand  with  red  mortar 
color,  in  order  to  make  the  brick  burn  darker.  Kindly  give 
me  all  the  information  you  can  on  this  subject,  as  the  sand 
I  use  burns  lighter  than  my  clay.  Kindly  inform  me,  as  near 
as  you  can,  what  proportion  of  the  coloring  matter  I  should 
use. 

The  quantity  of  red  coloring  matter  that  is  necessary 
to  bring  the  sand  to  the  right  color  after  it  is  burned, 
depends  upon  the  strength  of  the  pigment  used,  as  well 
as  on  the  quality  of  the  sand  and  the  kind  of  fuel  burned". 
The  better  way  is  to  experiment  with  a  small  batch  of 
brick,  keeping  a  careful  account  of  the  amount  of  color 
added  to  the  sand,  with  each  batch.  Another  way  is 


CLAYWORK1NG  PROBLEMS  lay 

described  by  Ellis  Lovejoy,  E.  M.,  in  an  answer  pub- 
lished more  than  a  year  ago  in  this  department.  In  it, 
he  said,  in  part:  "In  sand-molded  brick  we  have,  on 
several  occasions,  recommended  wetting  the  sand  with 
ferrous  sulphate  (copperas)  followed  by  drying.  This 
treatment  of  the  sand  produces  a  brilliant  red  color  and 
this  method  of  coloring  the  sand  for  the  molds  is  in 
practical  use." 


Cones  vs.  Pyrometers 

662.  Ohio — /  am  writing  to  you  as  to  a  "neutral"  to  clear 
up  a  point  that  is  gh-ing  me  considerable  -worry,  and  which 
surely  makes  me  doubt  the  accuracy  of  both  my  Seger  cones 
and  pyrometers.  I  formerly  used  cones  exclusively,  in  burn- 
ing my  product,  which  is  face-brick,  and  alu'ays  reached  cone 
1.  A  few  mouths  ago.  I  put  in  a  pyrometer  system,  and  since 
that  time  I  hare  stood  on  the  banks  of  the  River  of  Doubt. 
The  two  systems  do  not  check  and  I  do  not  know  which  is 
correct — if  either.  Professor  Orton's  cone  1  melts  at  2.102 
degrees  Fah.  according  to  the  table,  but  when  it  melts  in  my 
kiln,  the  temperature  reading,  according  to  the  pyrometer,  is 
usually  about  1.930  degrees  Fah.,  which  is  a  difference  of  172 
degrees.  Can  you  tell  me  how  to  correct  this,  and  whether 
the  cones  or  the  instrument  or  all  of  them,  are  at  fault?  I  am 
anxious  to  use  both,  as  the  cones  are  a  great  help  in  finish- 
ing our  burn  and  I  hare  found,  also,  that  our  firemen  take  a 
(/reat  deal  more  interest  in  their  work  since  they  arc  able  to 
TtYj/f/t  the  line  of  heat  advance  on  the  pyrometer. 

The  question  you  ask  is  an  old  one  and  one  that  is  bound 
to  come  up  periodically,  and  almost  always  when  anyone 
using  one  method  decides  to  use  the  other  also.  At  the  out- 
set, it  must  be  stated  that  the  cone  and  the  pyrometer  do  not 
do  the  same  work,  contrary  to  the  almost  general  opinion.  The 
cone  measures  the  result  of  heat.  The  pyrometer  measures 


CLAYWORKING  PROBLEMS 


temperature.  Professor  Orton  has,  possibly,  sent  you  a  list 
of  temperatures  at  which  the  cones  are  supposed  to  melt. 
They  may,  or  may  not  melt  at  that  particular  point, 
depending  upon  the  rate  of  firing,  the  quality  of  the 
kiln-gases,  etc.  He  also  undoubtedly  told  you  that  you 
should  think  in  cone  numbers,  not  in  temperatures,  when 
using  his  cones.  You  have  found  out,  by  experiment,  that 
your  ware  matures  and  is  at  its  best  point  at  the  time  cone 
1  falls  over,  providing  the  cone  is  in  the  same  position  in 
the  kiln  and  also  providing  that  the  kiln  is  burned  the  same 
way  each  time.  In  other  words,  you  have  found  that  the 
combination  of  circumstances  controlled  by  your  burns  has 
produced  a  certain  result  in  your  clay  brick  and  in  your  clay 
cone, — that  is.  that  they  both  mature  at  the  same  time.  This 
does  not  mean  that  they  both  mature  at  the  same  temperature, 
with  each  burn.  It  is  unfortunate  that  the  temperature  dif- 
ference ever  became  associated  with  cones.  The  cone  meas- 
ures heat-work-accomplishment,  and,  under  stated  conditions, 
and,  when  intelligently  used,  is  invaluable  to  any  common - 
clay  plant.  The  cone  indicates  when  the  ware  has  gone 
through  a  pyrometrical  change,  to  maturity.  The  pyrometer 
is  invaluable,  to  trace  the  temperature,  whether  rising  in  a 
burning  kiln,  or  falling  in  a  cooling  kiln.  It  indicates  the 
uniformity,  or  lack  of  uniformity  in  firing,  and  enables  the 
burner  to  know  whether  his  heat  is  falling,  is  stationary,  or 
is  rising.  Use  both  cones  and  pyrometer,  but  forget  abuui 
temperature  in  relation  to  the  cones. 


Quantity  of  Fire  Brick  for  Kiln  Crown 

659.  Illinois — Please  let  we  knoiv  how  many  fire-brick  it 
takes  to  put  a  crown  on  a  thirty  ft.  kiln  with  a  quarter  pitch, 
also  the  rule  yon  use  to  w<ork  the  calculation,  counting  twelve 
brick  to  the  foot. 

We  would   rather   give  you   the   rule   than   the   calculation ; 


CLAYWORKING  PROBLEMS  131 

it  is:  Multiply  15.5  by  the  rise  of  the  crown,  multiplied  by 
the  circumference  of  the  arch  formed  by  the  radius  of  the 
crown. 


Using  Steam  Shovels  in  Shallow  Work 

660.  Tennessee — Is  it  profitable  or  practical  to  work  a  clay 
pit  ivith  a  steam  shovel,  when  Irani  cars  are  used  and  the 
shovel  would  be  on  same  track?  The  bank  is  only  five  to  six 
feet  deep  and  there  is  an  eight  inch  to  ten  inch  stripping.  The 
daily  capacity  is  75,000  brick. 

A  plant  having  a  daily  capacity  of  75,000  brick  requires 
approximately  195  cubic  yards  of  clay  per  day.  A  small  steam 
shovel  should  dig  from  25  to  35  cubic  yards  per  hour  in 
shallow  work  or  a  minimum  of  250  yards  per  day  of  ten 
hours. 

Manufacturers  of  steam  shovels  contend  that  using  them  is 
both  practical  and  profitable  on  such  work  as  you  describe; 
these  claims  are  based  on  average  labor  costs.  If  your  labor 
cost  is  very  much  lower  than  the  average,  it  may  be  that  the 
figures  given  by  the  shovel  manufacturers  would  not  apply 
in  your  case,  but  the  chances  are  strongly  in  favor  of  the 
shovel  manufacturer. 


A  Kiln  to  Calcine  Fire  Clay 

663.  .Missouri — We  are  desirous  of  being  informed  as  ta 
the  most  practical  type  of  kiln  for  calcining  lump  fire-clay. 
The  clay  which  we  wish  to  calcine  is  a  plastic  clay  and  con- 
tains from  nine  to  twelve  per  cent  of  water.  We  desire  to  re- 
move the  lumps  direct  from  the  mine  and  place  them  in  the 
kiln.  In  doing  so,  they  will  not  have  time  to  air-slack.  In 
this  district,  it  is  the  custom  to  make  "dobies,"  which  are 
used  for  grog.  But  ive  are  under  the  impression  that  the 
yreat  amount  of  fine  clay  in  these  "dobies"  is  of  but  little 


CLAYWORK1NG  PROBLEMS 


value,  as  the  "dobies"  do  not  contain  the  original  sharp  cubes, 
(is  burnt  lumps  would  contain.     Jf'c  arc  therefore  desirous  of 


learning  of  a  practical  kiln,  which  will  calcine  approximately 
one   hundred  tons   of  fire-clay  daily.     Do   you  know  of  any 


CLAYWORKING  PROBLEMS  138 

kilns  in  operation  that  arc  doing  this,  and  which  have  condi- 
tions similar  to  ours? 

J.  Otto  Trautwein  has  given  us  the  sketch  that  is  printed 
below,  and  the  explanation  that  follows  it. 

"There  seems  to  be  no  reason  why  plastic  fire-clay,  contain- 
ing from  nine  to  twelve  per  cent  of  water,  could  not  be  cal- 
cined continuously,  on  the  same  principle  as  that  used  in  a 
blast  furnace.  The  fire-clay  could  be  fed  in  at  the  top,  by 
means  of  an  elevator  or  conveyor,  and  peep-holes,  placed  in 
the  hopper  and  in  the  kiln  between  the  fire-boxes,  would  show 
how  rapidly  the  calcining  process  was  progressing.'' 


Wants  Fire  Brick  Dimensions 

•>.">:{.  California — U'e  have  noticed  frith  interest  your  ra/w- 
nblc  table  published  in  the  Superintendent's  Department  of 
the  March  16  issue.  If  it  is  agreeable  to  you.  we  should  like 
to  use  this  in  a  price-list  which  we  will  issue  within  a  fezt- 
months.  Will  you  kindly  gire  us  the  dimensions  of  the  key. 
arch  and  wedge  brick  used  in  your  tables? 

We  will  be  very  glad  to  have  our  readers  use  this  table 
in  their  printed  matter,  if  it  is  useful  to  them.  The  sizes 
used  were  as  follows : 

No.  1  Key— 9x2^  thick  x  4y>  to  4  wide  =112  brick  to 
circle  12  ft.  inside  diameter. 

No.  2  Key — 9x2^  thick  x  4!/>  to  :\V>  wide  =  «5  brick  to 
:ircle  6  ft.  inside  diameter. 

No.  3  Key — 9x2^  thick  x  4J/2  to  3  wide  =  41  brick  to  circle 
:s  ft.  inside  diameter. 

No.  4  Key— 9x2 Vi  thick  x  \V2  to  2'4  wide  =  2rt  brick  to 
circle  \y2  ft.  inside  diameter. 

No.  1  Wedge — 9x4^2  wide  x  V/2  to  2  thick,  tapering  length- 
wise =  102  brick  to  circle  5  ft.  inside  diameter. 

No.  2  Wedge— 9x4^x2^2  to  \V2  thick  =  63  brick  to  circle 


134  CLAYWORKING  PROBLEMS 


2Vj  ft.  inside  diameter. 

No.  1  Arch — 9x4^x2^  to  2  thick,  tapering  breadthwise  = 
72  brick  to  circle  4  ft.  inside  diameter. 

No.  2  Arch— 9x4^x2*4  to  1 1/2  —  42  brick  to  circle  2  ft. 
inside  diameter. 


Absorption  Tests  on  Face-Brick 

(>54.  Illinois — fVry  recently  the  writer  was  led  into  a  dis- 
cussion relative  to  the  absorption  test  on  various  kinds  of 
face-brick.  Not  being  thoroughly  versed  on  the  subject,  I 
could  not  hold  up  my  end  of  the  conversation  as  I  would 
hare  wished.  U'ill  yon  give  me  what  information  you  have 
as  to  the  method  of  making  absorption  tests,  their  value  and 
the  best  way  of  making  use  of  the  results  of  these  tests  in 
connection  with  the  sale  of  face-brick ? 

The  most  common  way  of  making  an  absorption  test  is  to 
first  dry  the  brick  to  be  tested— particularly  if  it  has  been 
taken  from  a  pile  that  has  stood  out-of-doors  for  any  length 
of  time.  The  drying  can  be  done  in  the  oven  of  an  ordinary 
cook-stove.  Second— it  should  lie  accurately  weighed.  Third 
— it  should  be  immersed  in  water  for  at  least  twenty-four 
hours.  Fourth — it  should  be  wiped  with  a  soft-cloth  or 
sponge,  to  remove  all  "surface  water.1'  Fifth — it  should  be 
again  weighed,  and  with  the  same  care  for  accuracy.  The 
process  may  be  varied,  according  to  the  severity  of  the  test 
required,  by  substituting  a  three-quarter  immersion  for  a 
complete  immersion,  the  former  filling  the  pores  more  accu- 
rately, since  the  water  is  absorbed  by  capilliary  attraction, 
while  the  air  escapes  from  the  upper  and  non-immersed  sur- 
faces. Or — still  another  variation — immerse  the  brick  for 
twelve  hours,  bringing  the  water  to  a  boiling  point  during 
the  last  part  of  the  twelve  hour  period  and  continuing  it  at 
a  boil  for  not  less  than  half  an  hour.  This  opens  up  pores 
in  the  brick  that  would  otherwise  remain  closed. 

Regarding   the   value   of   these   tests— this   is   problematical. 


CLAYWORKING  PROBLEMS  135 


The  true  test  of  the  value  of  face-brick  lies  in  its  ability  to 
make  a  dry  wall,  and  to  keep  its  face  clean.  A  dry-press 
brick,  absorbent  to  a  great  degree,  yet  flashed  on  its  face, 
back  and  heads,  will  accomplish  these  purposes  quite  as  well 
(and  it  is  claimed,  better  )than  the  most  impervious  of  stiff- 
mud  brick.  When  the  question  of  efflorescence  is  raised, 
there  is  little  choice  between  a  brick  that  extracts  the  free 
lime  from  the  mortar,  bringing  it  out  at  the  center  of  the 
brick,  and  spreading  it  toward  the  edges,  as  against  a  brick 
that,  while  itself  neutral,  still  receives  the  limey  deposit  from 
the  motor  joint,  and  shows  the  white  discoloration  after 
every  warm,  rainy  spell.  The  value  of  the  absorption  test 
is  not  nearly  so  great  as  the  value  of  the  "time  and  use" 
test,  which  can  be  shown  a  prospective  customer  in  the  house 
where  the  brick  you  are  selling  him  was  used — perhaps  some 
years  ago.  That  will  tell  him,  if  he  has  a  grain  of  common 
sense,  more  than  he  can  learn  from  these  absorption  tests, 
which  are  not  practical,  in  that  they  do  not  approximate  any 
of  the  conditions  that  the  brick  is  to  meet  in  its  daily  work. 
The  principle  lying  back  of  the  effectiveness  of  the  "best 
by  time's  test"  demonstration  is  the  old  one  of  "seeing  is 
believing,"  and  while  the  laboratory  test  might  appeal  to 
the  imagination  of  some  people,  the  vast  majority  is  gen- 
erally more  easily  and  positively  convinced  by  actual  re- 
sults. 

As  to  the  best  way  of  using  these  tests  in  the  marketing 
of  face-brick,  we  think  that  you  should  demand  a  real  absorp- 
tion test,  made  along  the  lines  suggested,  every  time  your 
competitor  tries  the  time-honored  (but  otherwise  without 
honor)  method  of  pouring  a  teaspoonful  of  water  on  the 
face  of  his  (and  your)  brick,  and  then  "leading''  the  little 
lake  along  the  line  that  shows  in  the  face  of  your  brick,  and 
where  your  brick  has  the  greatest  porosity,  and  away  from 


C L A Y W ORKI NG  P K O  B  L EM S 


the  same  line   in  his  own  brick,  although   he  knows,  as   well 
as  you  do.  that  he  is  trying  to  cheat. 


Dipping  Brick  to  Change  Color 

627.  Indiana — Is  there  any  way  to  get  different  colors  on 
the  face  of  brick  by  dipping  them  and  then  burning ? 

In  order  to  answer  this  question  intelligently,  it  would  be 
necessary  for  us  to  have  a  piece  of  the  brick  that  you  desire 
to  make  in  a  different  color  and  a  very  exact  statement  of 
the  process  that  you  use,  beginning  with  the  manner  in  which 
your  clay  is  harvested  up  to  the  point  of  the  kind  of  fuel 
used  in  its  burning  and  the  time  which  you  give  to  water- 
smoking,  burning  and  cooling. 


Dipping  Brick  to  Change  Color 

627.  Indiana — Is  there  any  way  to  get  different  colors  on 
the  face  of  brick  by  dipping  them  and  then  burning? 

The  above  question  was  published  in  the  April  6  issue,  and 
a  suggestion  made  that  it  would  be  necessary  for  this  cor- 
respondent to  send  us  a  piece  of  the  brick  that  he  wanted 
to  change  in  color  by  the  dipping  process,  and  also  an  exact 
statement  of  his  process  of  manufacture. 

Since  publishing  this,  we  have  received  a  letter  from  James 
Witte,  of  618  South  Main  Street,  Salt  Lake  City,  Utah,  which 
reads  as  follows : 

"I  have  a  process  by  which  any  desired  color  can  be  made 
no  matter  what  color  the  brick  ordinarily  burns.  This  color 
is  given  by  either  dipping  the  brick  or  spraying  it  with  cer- 
tain chemicals  that  are  inexpensive.  I  can  adapt  these  chem- 
icals to  become  sufficiently  fluxed  to  enable  them  to  set  well 
on  the  brick,  making  the  face  impervious  to  mcisture.  Up  to 
the  present  time  I  have  worked  out  a  pure  white,  a  gray,  a 
light  blue,  a  dark  blue,  a  dark  brown  and  a  sage  green.  To 


CLAYWORKING  PROBLEMS  137 

the  best  of  my  knowledge.  I  am  the  first  one  to  work  this 
process,  which  can  be  used  with  any  color  of  clay.  I  have 
been  successful  in  putting  this  surface  on  red  brick  at  cone 
4, — 1,958  degrees  Fah.,  and  am  now  putting  it  on  a  red 
burning  sewer-pipe  clay  at  cone  8, — 2,354  degrees  Fah.  I  am 
an  expert  in  enameled  brick  manufacture,  also  porcelain 
face-brick  and  have  had  a  life-long  experience  in  the  making 
of  enamels.  I  am  prepared  to  sell  my  formulas  and  will  be 
glad  to  correspond  with  the  manufacturer  whose  question 
you  published." 


Coloring  Matter  Used  in  Clayworking 

652.  New  York — The  appearance  of  an  advertisement  for 
rough-cut  brick,  printed  in  colors  in  a  recent  issue  of  "Brick 
tind  Clay  Record"  prompts  me  to  ask  just  how  extensive  is 
the  demand  for  artificial  colored  brick  and  the  probable  quan- 
tity of  color  used  annually  by  brick,  architectural  terra-cotta 
(ind  art  tile  manufacturers.  Also  whether  this  demand  for 
artificially  colored  burned  clay  products  is  increasing,  stag- 
nant or  decreasing.  As  everybody  knows,  coloring  agents  are 
particularly  hard  to  get,  at  the  present  time — that  is,  coloring 
agents  that  emanate  from  coal  tar.  What  I  would  like  to 
know  is  whether  natural  earth  colors  or  coal  tar  colors  are 
used  in  the  various  clay  products  lines.  I  would  also  like  to 
learn  from  first-hand  sources,  whether  brick  manufacturers 
in  particular  are  especially  interested  in  bringing  out  new 
colors  in  their  lines  of  brick,  like  green,  for  instance;  ivould 
there  be  any  great  demand  for  brick  with  these  out-of-thc- 
iirdinary  shades?  Do  common-brick  manufacturers  use  red 
coloring  matter  to  any  extent?  What  degree  of  heat  would 
these  coloring  materials  have  to  withstand? 

In  the  brick  industry  red  hematite  is  used  extensively  for 
the  giving  of  a  uniform  red  color  to  common  building  brick. 
It  is  mixed  with  molding  sand  and  put  on  the  surface  of 
each  brick  where  it  forms  but  a  small  portion  of  a  very  thin 


CLAY  WORKING  PROF.  I. EMS 


film.  One  concern  with  an  output  of  about  twenty  million 
brick  per  year  uses  one  carload  of  red  hematite  every  two 
years. 

In  the  architectural  terra-cotta  industry  the  only  artificial 
colors  used  are  those  employed  by  potters  and  what  these 
consist  of  can  be  readily  learned  by  the  investigation  of 
glazes  in  common  use.  Here  again  it  will  be  found  that  the 
amount  of  color  is  very  small  compared  to  the  bulk  of  the 
finished  product  as  the  coloring  agent  forms  but  a  small  part 
of  the  thin  film  on  the  surface  of  the  terra-cotta. 

In  face  brick,  oxide  of  manganese  has  been  used  for  many 
years  in  order  to  give  the  gray  tinge  to  fire  clay  brick  which 
would  otherwise  be  a  buff-white  color.  This  manganese, 
if  in  powdered  form,  gives  a  pepper-like  speckle  which  at  a 
very  short  distance  becomes  a  solid  gray.  When  used  in 
larger  lumps,  it  gives  a  more  speckled  appearance  and  in  this 
way  accents  the  white  ground.  It  has  been  calculated  that 
the  addition  of  manganese  increases  the  cost  of  making  brick- 
by  about  two  dollars  per  thousand  and  since  many  factories 
making  the  kind  of  face  brick  to  which  manganese  can  be 
added,  figure  their  cost  of  production  at  between  nine  and 
eleven  dollars  per  thousand,  you  will  see  that  the  use  of 
manganese  is  a  rather  expensive  proposition. 

For  many  years  theorists  have  figured  that  a  green  brick 
— a  brick  which  would  be  naturally  green,  not  "go  green"  in 
the  wall — would  lie  welcomed  by  architects.  There  is  no 
knowing,  however,  what  sort  of  a  reception  it  would  get  and 
if  it  carried  a  high  price,  the  chances  are  that  it  would  re- 
ceive a  very  cold  shoulder.  So  far  as  our  knowledge  goes, 
coal  tar  by-products  have  never  been  used  in  connection  with 
the  brickmaking  industry — the  reason  being  that  no  coal  tar 
dyes  could  withstand  the  degree  of  heat  necessary  to  mature 
the  brick. 

In  the  manufacture  of  the  rough-cut  brick  advertised  in 
the  recent  issue  of  "Brick  and  Clay  Record"  which  advertise- 
ment was  printed  in  colors,  would  say  that  these  brick  are 


CLAYWORKING  PROBLEMS  139 

burned  at  from  1,800  to  2,100  degrees  F.  No  artificial  color- 
ing matter  is  added,  the  color  being  produced  solely  by  the 
action  of  a  reducing  atmosphere  in  the  kiln.  It  is  much 
cheaper  to  close  the  dampers  and  allow  the  smoke  and  fumes 
from  the  coal  to  act  upon  the  brick  than  it  is  to  add  any 
coloring  matter  to  it.  Brick  made  from  fire-clay — which  are 
the  kind  of  brick  to  which  manganese  is  added — are  burned 
to  2,200  degrees  F.  and  sometimes  beyond  that  point. 

The  question  asked  opens  some  interesting  points,  how- 
ever, and  "Brick  and  Clay  Record"  will  welcome  any  cor- 
respondence which  might  come  from  those  experienced  in  the 
use  of  artificial  colors  in  the  manufacture  of  any  burned  clay 
product. 


Wants  Information  as  to  Stack  Area 

645.  Minnesota — 7  am  thinking  of  putting  in  down-draft 
round  kilns,  thirty  feet  in  diameter  and  holding  100,000  brick. 
There  will  be  ten  fire  places,  which  allows  one  fire  place  for 
each  10,000  brick.  How  much  grate  surface  would  be  re- 
quired for  each  fire  place?  I  am  using  two  square  feet  of 
<irate  surface  in  each  fire  place  in  my  scove  kilns  and  figure 
on  10,000  brick  to  each  fire  place.  What  size  chimney  would 
vou  recommend  using?  I  would  want  to  use  one  chimney 
for  two  kilns,  arranging  it  so  that  I  could  use  it  on  one  kiln 
fit  a  time.  The  yard  is  pretty  well  out  in  the  open  and  is  on 
i  high  bank. 

Regarding  the  size  of  a  chimney  or  stack  to  use  with  a  30- 
ft.  down-draft  kiln,  would  say  that  we  recommend  3  ft.  by 
">  ft.  9  in.  inside  measurements  with  a  9  in.  spider  or  separat- 
ing wall  running  up  the  middle.  This  will  leave  the  inside 
stack  area  for  each  kiln  2  ft.  6  in.  by  3  ft.  The  object  of  the 
spider  is  to  prevent  the  draft  of  one  kiln  from  interfering 
with  the  other.  The  spider  does  not  in  all  cases  go  to  the 
top  of  the  stack  but  it  should  go  up  at  least  10  ft.  from  the 


CLAYWORKING  PROBLEMS 


base  and  should  he  not  less  than  one-third  of  the  stack 
high. 

You  speak  of  putting  in  two  round,  down-draft  kilns,  each 
of  30  ft.  diameter  and  each  holding  100,000  brick.  Are  you 
at  all  certain  that  you  will  succeed  in  setting  100,000  hrick  in 
a  30  ft.  diameter  kiln? 

Regarding  the  grate  surface,  we  would  suggest  that  you 
allow  five  square  feet  to  each  furnace  and  that  your  stack  he 
not  less  than  3.i  ft.  high. 


Clay  Bar  "Feathers  " 

64(i.  \'orth  Carolina — IV c  arc  having  trouble  isith  our 
brick  machine  which  causes  the  clay  bar  to  "feather"  or 
crack  on  one  or  more  of  the  edges  as  it  comes  from  the  die. 
Our  clay  has  a  high  percentage  of  shale  and  we  use  an  oil 
die,  the  column  coming  out  of  the  machine  edgeways. 

The  "feathering''  may  he  caused  by  any  of  several  reasons, 
of  which  insufficient  tempering  or  its  opposite  extreme — too 
much  tempering— may  be  one;  insufficient  lubrication  may  be 
another ;  the  die  may  be  too  short  or  too  long ;  the  clay  bar 
may  be  too  soft.  The  most  probable  cause  is  lack  of  uniform 
lubrication  in  the  corners  of  the  die.  This  probably  causes 
friction  and  consequent  holding  back  of  the  corners  of  the 
column.  This  difference  in  the  flow  of  the  bar  causes  strains 
to  be  set  up  that  invariably  tear  or  "feather"  the  edges.  Why 
not  write  to  the  manufacturers  of  the  die  that  you  use,  tell- 
ing them  of  your  trouble  and  asking  them  to  suggest  a 
remedv? 


Best  Height  for  Kiln  Crown 

(547.     Pennsylvania — H'hat  is  the  lowest  height  of  spring  it 
would  be  practical  to  use  for  a  crown  of  a  thirty-five  foot  in- 


CLAYWORKING  PROBLEMS  141 


side  diameter  sewer  pipe  kiln;  the  crown  being  built  of  twelve 
inch  fire  brick  and  banding  no  object. 

It  appears  that  you  wish  to  secure  as  flat  an  arch  as  pos- 
sible and.  at  the  same  time,  be  sure  that  it  is  safe.  The 
thrust  of  an  arch  on  kiln  walls  and  kiln  bands  is  not  the  only 
point  to  be  considered.  If  the  arch  is  too  high  or  too  low. 
the  tendency  to  buckle  and  to  warp  is  great — this  tendency 
usually  manifesting  itself  on  the  quarters.  The  smaller  the 
perpendicular  distance  between  the  spring  of  the  arch  and 
the  apex  of  the  crown,  the  stronger  must  be  the  kiln  bands. 

A  height  of  8  ft.  6  in.,  or  approximately  one-quarter  of 
the  inside  diameter  of  the  kiln,  is  generally  accepted  as  the 
best  practice,  for  it  has  been  found  that  the  kiln  crown  re- 
sists deformation  strains  when  the  rise  is  as  noted.  If  you 
wish  a  lower  crown  in  order  to  confine  the  heat,  the  best 
method  is  to  lower  the  kiln  side  walls.  This  procedure  will 
not  materially  decrease  the  capacity  of  the  kiln.  One  thing 
must  be  borne  in  mind— that  is  to  secure  a  sufficient  curve 
in  the  crown  to  create  a  tendency  to  resume  its  original  con- 
tour after  expansion. 


Burning  Lignite  in  Down  Draft  Kilns. 

633.  West  Virginia — /  have  a  brick  plant  proposition  under 
way  where  it  ai'//  be  economical  to  use  lignite  coal.  Will 
you  give  me  what  information  you  have  regarding  the  prac- 
ticability of  using  lignite  coal  in  burning  brick,  especially  in 
down-draft  kilns? 

This  is  an  important  question — important  because  fifty  per 
cent  of  the  balance  of  our  coal  supply  is  lignite.  Here  is  a 
material  which,  generally  speaking,  is  considered  a  low  grade 
fuel:  within  it  a  great  tonnage  of  immense  commercial  value 
lies  dormant.  Lignite  runs  low  in  carbon  or  heat  producing 
constituents,  high  in  volatile  matter,  high  in  moisture.  In 
the  volatile  matter  we  find  a  commercial  product  that  has 
many  times  the  value  of  the  carbon  that  is  missing.  In  all 


CLAYVVORKING  PROBLEMS 


direct  firing  of  lignite  we  must  make  allowances  for  the  loss 
of  the  heat  which  is  used  in  evaporating  the  free  moisture, 
and  any  attempt  to  use  raw  lignite  in  ordinary  direct  firing 
cannot  help  but  result  in  low  efficiency.  Since,  however,  our 
questioner  may  be  compelled  to  follow  the  old  methods  of 
firing,  we  will  endeavor  to  show,  as  accurately  as  is  possible, 
the  construction  of  a  fire-box  for  lignite  and  compare  it  with 
the  fire-box  that  is  often  used  to  burn  bituminous  coal. 

For  example,  using  a  12.000  B.T.U.  bituminous  coal  and 
8,000  B.T.U.  lignite — in  the  former,  with  a  certain  draft,  we 
would  consume  to  an  ash  approximately  10  Ib.  of  coal  per 
sq.  ft.  and,  at  100%  efficiency,  in  a  6'  0"  grate,  or  3  sq.  ft.  of 
grate  area,  we  would  liberate  720.000  B.T.U.  (6X10X12.0001 
per  fire  box  per  hour,  or,  for  a  twelve  fire  box  kiln,  8,640,000 
B.T.U.  per  hour,  to  obtain  the  required  temperature.  To 
produce  the  same  results  with  lignite,  we  would  increase 
llie  grate  area  so  as  to  consume  that  quantity  of  lignite  which 
would  be  required  to  produce  the  same  quantity  of  heat  per 
hour,  or  720,000+8,000+10=9  sq.  ft.,  instead  of  6. 

Provision  should  also  be  made  for  the  proper  air  supply 
and  for  equal  distribution  over  the  greater  grate  area,  and 
also  it  will  add  greatly  to  the  efficiency  if  this  air  is  super- 
heated and  supplied  by  blast.  Every  brick  yard  has  an 
abundant  supply  of  waste  heat  so  that  simple  and  effective 
means  could  be  provided  for  supplying  superheated  air  for 
all  combustion  and  the  result  produced  would  pay  for  the 
extra  expense  in  a  very  short  time. 

It  would  be  well  for  all  who  contemplate  the  use  of  lig- 
nite in  direct  firing,  and  especially  those  not  familiar  with  its 
use,  to  correspond  with  Mr.  Russell,  manager  of  the  Dicken- 
son  Fire  &  Pressed  Brick  Company,  of  Dickenson,  N.  Dak. 
Mr.  Russell  has  had  years  of  practical  experience  with  lignite 
in  the  burning  of  common-brick  and  fire-clay  products,  is 
a  technical  man  and  should  furnish  valuable  practical  infor- 
mation. We  cannot  help  but  believe,  however,  that  all  pres- 
ent methods,  which  consume  the  total  quantity  of  raw  or 


CLAYWORKING  PROBLEMS  143 

bituminous  coal  with  such  tremendous  loss,  are  entirely 
wrong  and  not  in  keeping  with  well  established  scientific 
methods. 

All  of  our  lignite  coal  fields  are  found  in  the  far  West 
and  Northwest,  where  other  fuel  is  scarce  and  high  priced, 
due  to  the  long  freight  haul.  If  the  most  economical  methods 
are  sought,  then  the  best  results  up  to  date  can  be  had  by 
adopting  or  erecting  a  lignite  carbonization  plant  similar  to 
the  one  operating  at  Minot,  N.  Dak.,  in  which  it  requires 
about  two-and-one-eighth  tons  of  raw  lignite  carbonized 
to  make  one  ton  of  high  carbon  briquettes.  The  briquetted 
carbon  will  practically  have  the  same  heating  value  as  anthra- 
cite and  commands  about  the  same  price,  and  about  $1.50  to 
$2.00  net  per  ton  of  briquette  can  be  made  in  the  process, 
while  letting  all  of  the  gas  escape  to  the  atmosphere. 

The  process  will  produce  from  12,000  to  15,000  ft.  of  400 
B.T.U.  gas  per  ton  of  briquettes,  or  from  4,800,000  to  6,000,- 
000  B.T.U.  of  available  gas  which  could  be  used  in  the  ourn- 
ing  of  clay  products.  This  method  was  established  by  Prof. 
E.  J.  Babcock,  dean  of  the  School  of  Mining  Engineering,  at 
Grand  Forks,  N.  Dak.,  and  is  giving  very  good  results.  But 
as  it  is  the  retort  method  and  periodic,  it  is  to  be  hoped  it 
will  not  be  long  until  further  developments  will  result  in  a 
continuous  and  automatic  process  which  will  be  more  eco- 
nomical and  less  expensive  to  construct. 

Clay  products  manufacturers,  like  the  steel  products  people, 
must  devise  and  adopt  a  by-product  process  so  as  to  not 
only  provide  economical  fuel  that  can  be  applied  in  a  man- 
ner that  will  produce  the  best  results,  but  assist  in  the  elimi- 
nation of  our  wholesale  waste  of  natural  resources.  No 
smelter  can  successfully  operate  without  coke.  Coke  is  of  a 
certain  structure  which  supports  the  ore  during  the  smelting 
process.  Hence  they  erect  coke  oven  by-product  plants,  and 
their  by-products  are  gas,  ammonium  sulphate,  tar,  etc.  The 
clay  product  manufacturers  require  gas  that  is  cool,  rich  and 
clean,  so  that  it  can  be  put  under  pressure,  and  a  valve  con- 


144  CLAY  WORKING  PROBLEMS 

trol   which   gives   them    full   control   of   the   temperature,    re- 
sulting in  a  uniform  product. 

To  get  that  kind  of  a  fuel  economically  they  should  erect 
gas  by-product  plants.  They  would  be  highly  profitable  and 
are  found  to  be  practical  by  manufacturers  in  other  lines 
that  depend  upon  heat  for  the  production  of  their  wares. 

The  above  question  was  published  in  the  Feb.  2,  1915, 
issue  and  an  answer  given  at  that  time  which  was  written 
by  one  of  the  best  known  exponents  of  the  adaptability  of 
low  grade  coal  burning  in  the  manufacture  of  clay  ware. 

A  subscriber  has  written,  protesting  against  some  of  the 
statements  that  were  made  and,  as  his  remarks  are  evidently 
those  of  a  man  who  knows,  we  print  them,  without  altera- 
tion, addition  or  omission.  He  writes: 

"The  writer  notes  in  the  Feb.  2  issue  the  answer  you  have 
made  to  '633  \Yest  Virginia'  on  the  subject  of  burning 
lignite  coal.  In  this  answer  you  suggest  that,  for  an  eco- 
nomical method,  a  plant  should  be  erected  similar  to  the 
one  operating  at  Minot.  No.  Dak.,  where  lignite  is  carbon- 
ized and  briquetted. 

"Perhaps  this  is  none  of  the  writer's  business,  but  for 
the  good  of  the  clay  working  fraternity,  he  feels  called  upon 
to  suggest  that  the  man  who  wrote  the  answer  might  well 
make  a  more  extended  investigation  at  Minot  and  that  when 
lie  has  done  so,  he  will  not  be  so  apt  to  ask  other  people  to 
invest  their  money  in  a  similar  proposition. 

"The  plant  which  the  writer  is  running  is  burning  raw 
lignite  in  the  manufacture  of  brick  and  is  getting  good  re- 
sults in  burning  common  brick  in  up-draft  kilns.  It  is  not. 
however,  giving  satisfactory  results  with  pressed  brick  in 
down-draft  kilns,  although  we  expect  to  get  better  results 
by  building  larger  stacks. 

"We  use  fans,  and  when  we  built,  were  advised  that,  on 
account  of  using  forced  draft,  we  would  not  need  to  build 


CLAYWORK1NG  PROBLEMS 


high  stacks.  We  think  different  now,  for  we  cannot  get  rid 
of  the  moisture  without  trouble  and  loss  of  time. 

"We  are  awaiting  further  developments  in  the  carboniz- 
ing of  lignite  and  the  use  of  by-products  before  putting  any 
more  money  into  the  'game'.  At  the  present  time,  the  best 
proposition  in  this  line  is  the  kind  of  carbonizing  plant  built 
by  Professor  S.  M.  Darling  of  Estevan,  Sask.,  who  built  an 
experimental  plant  at  Estevan  for  the  Saskatchewan  govern- 
ment. He  has  just  issued  his  report,  a  copy  of  which  may  be 
secured  by  writing  to  the  government  office  at  Regina,  Sask. 

"The  writer  has  examined  the  plant  at  Minot  and  is  pre- 
pared to  say  that  the  methods  in  use  there  are  crude  and 
expensive  and  not  in  any  way  satisfactory.  This  is  largely- 
due  to  the  fact  that  the  product  is  not  and  cannot  be  held 
uniform.  This  is  as  bad,  comparatively,  as  it  would  be  for 
one  of  the  large  flour  mills  to  make  an  hourly  change  in  its 
grade  of  wheat  or  in  its  mixture.  The  change  is  reflected 
in  the  finished  product  as  well  as  in  the  cost  of  operation. 

"At  Minot  every  car  of  carbonized  lignite  is  different. 
This  results  in  a  constant  endeavor  to  meet  conditions  by 
change  of  binder  necessary  and  by  other  mechanical  shifts 
and  there  is  no  doubt  but  that  a  large  sum  of  money  must 
have  been  lost  there  during  the  past  year,  in  what  seems  to 
be  a  vain  endeavor  to  make  briquettes. 

"The  Darling  plant  at  Estavan  was  in  continuous  operation 
and  a  uniform  carbon  resulted.  This  finished  carbon  has 
been  used  with  great  success  in  gas  producer  engines.  Pro- 
fessor Darling  has  built  no  briquetting  station  but  has 
shipped  his  product  to  other  plants  where  good  briquettes 
have  been  made  and  there  seems  no  doubt  but  that  he  has 
the  right  idea. 

"In  conclusion  I  would  ask  that  you  give  this  letter  as 
much  publicity  as  possible,  for  the  reason  that  I  believe  that 
whoever  wrote  the  answer  to  the  original  question  was 
ignorant  of  the  exact  state  of  affairs  at  Minot  and  has  been 
careless  enough  to  pass  hearsay  information  to  your  readers. 


CLAYWORK1NG  PROBLEMS 


If  they  in  turn  acted  upon  his  suggestions,  without  making 
a  personal  examination  of  the  plant,  property  and  product 
that  he  praised  so  highly,  the  result  would  he  an  enormous 
additional  pecuniary  loss." 


To  Make  Bullnoses  by  Hand. 

(W5.    North  Carolina — Please  give  us  a  suggestion  as  to  the 


TEMPLA 
BOX 


best  method  for  cutting  the  corner  of  bullnosc  brick.     Ours  is 
an  end  cut  machine. 

Bullnoses   can   he   cut   by   hand  in   hullnose  template  boxes. 


CLAYWQRKING  PROBLEMS  147 

which  are  made  like  sketch  herewith.  The  standard  size 
green  brick  is  placed  in  this  box,  which  is  arranged  so  that 
the  sides  will  fit  the  beds  of  the  brick  very  snugly.  A  cut- 
ting wire  strung  on  a  bow,  or  a  sharp  knife  is  used  to  trim 
the  former  to  the  same  radius  as  the  sides  of  the  box  and 
the  brick  is  removed  and  smoothed  up  with  the  aid  of  a 
scalpel  knife  and  a  pan  of  water.  One  man  can  turn  out  about 
five  hundred  of  these  brick  in  a  day,  the  number  depending 
upon  his  ability  and  the  character  of  the  clay  he  is  work- 
ing, as  well  as  the  exactness  of  the  finish  required. 


Economy  of  Various  Grades  of  Coal. 

603.  Montana — Figuring  coal  screenings  worth  $1.00  per 
ton,  pea  size  at  $2.00  and  nut  at  $2.75,  which  grade  is  the 
cheapest  to  use  in  a  scove  kiln.  Also  how  long  should  grates 
be  and  what  style?  What  kind  erf  coal  do  you  recommend 
zvhere  a  burner  has  the  choice  between  a  hot,  flashy  coal  that 
has  very  little  ash  and  a  slower  acting  coal  with  considerable 
ash.  Both  coals  burn  without  clinkering  and  the  B.  t.  it's 
are  about  the  same? 

The  cost  of  fuel  is  determined  by  points  other  than  the 
initial  cost  per  ton.  Time  is  a  consideration,  for  it  affects 
capacity  and  labor  cost.  The  quality  of  the  ware  is  also 
to  be  considered,  since  this  affects  the  selling  price.  The 
coal  that  combines  the  small  tonnage  to  mature  the  ware 
in  the  shortest  time  with  the  highest  percentage  of  first 
quality  ware  is.  as  a  rule,  the  cheapest,  irrespective  of 
its  cost  per  ton.  This  statement  is  subject  to  some  cor- 
rection, since  there  might  be  so  wide  a  difference  be- 
tween one  initial  cost  and  another  as  to  off-set  the  sav- 
ing in  time,  labor,  repairs  and  spoiled  ware.  To  secure 
a  solution  to  your  problem,  it  will  be  necessary  for  you  to 
keep  records— records  that  will  show  the  length  of  time 
taken  to  complete  each  burn,  the  quality  and  quantity  of 
material  burned  and  the  cost  of  the  fuel.  You  are  fortunate- 


CLAYWORKING  PROBLEMS 


ly  situated  in  this  regard  in  that  all  of  the  coal  mentioned 
by  you  has  practically  the  same  B.  t.  u.  value.  Generally 
speaking,  hot  flashy  coal  with  little  ash  is  preferable  to  the 
slower  acting  coal  that  has  more  ash,  but  this  again  depend? 
upon  local  conditions.  It  may  be  a  good  plan  to  place  peep 
holes  through  the  side  of  the  kiln  wall,  spacing  them  two 
feet  apart  from  bottom  to  top.  Through  these  the  advance 
or  the  raising  of  the  heat  can  be  seen  and  records  made  that 
will  have  a  bearing  upon  your  final  decision.  A  comparison 
of  the  data  thus  obtained  should  bring  reliable  information. 
It  is  impossible  to  answer  your  question  regarding  grates 
as  the  size  and  style  depend  upon  the  fuel  you  intend  using. 
The  dimensions  also  depend  upon  the  construction  of  the 
kiln  and  the  furnaces.  Sometimes  the  coal  burning  fur- 
naces are  entirely  away  from  the  arch,  in  a  side  wall  of  the 
kiln  and  are,  at  times,  placed  in  extensions  b.uilt  out  from 
this  wall.  It  is  very  difficult  to  give  any  positive  answer 
to  the  problem  as  it  has  so  many  angles,  anyone  of  which 
might  off-set  another. 

The  Burning  of  Alkaline  Clay. 

62'2.  Montana — Is  there  a  sure  way  of  burning  good  brick 
from  clay  that  contains  alkali,  potash,  etc.?  I  mean,  is  there 
a  way  to  get  them  hard  and  yet  keep  them  from  fusing  to- 
gether? Is  it  true  that  a  kiln  can  be  handled  so  that  the 
alkaline  salts  will  be  dissipated  before  settling  takes  place  and 
so  be  absent  at  that  part  of  the  burning  period  where  they 
would,  if  present,  act  as  a  flux? 

This  depends  entirely  on  the  percentage  contained  of  each 
mineral  mentioned.  If  it  be  excessive  then  we  know  of  no 
way  to  accomplish  the  burning  in  safety.  We  do  not  believe 
that  it  is  true  that  these  salts  can  be  so  changed  during  any 
part  of  the  water  smoking  or  burning  period  that  they  would 
be  rendered  harmless.  The  only  change  that  could  take 
place,  so  far  as  we  know,  is  that  which  would  occur  when 


CLAYWORK1NG  PROBLEMS  149 

they  had  attained  sufficient  heat  to  become  chemically  active, 
fluxing  and  fusing  and  attracting  the  surrounding  silicates, 
hut  this  change  is  the  very  one  you  wish  to  avoid.  We 
would  like  to  have  more  information  on  this  point  from  our 
readers. 


Coloring  Molding  Sand. 

610.  Minnesota — There  are  brick  yards  in  this  vicinity 
turning  out  the  same  kind  of  brick  that  I  am  making  but 
they  use  a  certain  coloring  matter  in  the  molding  sand  that 
•fires  all  of  their  brick  a  dark  red  color.  It  will  please  me 
<ireatly  if  you  can  tell  me  what  they  use  and  how  it  is  done. 
It  is  only  the  molding  sand  they  color  and  it  would  aid  me 
considerably  if  I  knew  zvhat  they  used  and  how  to  use  it. 

The  material  that  you  want  for  this  purpose  is  ordinary 
red  mortar  color  in  dry  powdered  form.  Slight  experiment- 
ing will  teach  you  how  much  to  mix  with  your  molding  sand 
and  in  this  connection,  would  say  that  only  a  small  quantity 
is  required.  Regarding  the  best  way  of  applying  the  molding 
sand  mixed  with  the  color,  we  refer  you  to  the  article  pub- 
lished in  the  July  7.  1914.  issue  of  "Brick  and  Clay  Record" 
(page  58). 

Wants  to  Mix  Shale  with  Surface  Clay 

644.  Iowa — Jl'f  have  a  stratum  of  shale  under  thirty  to 
forty  feet  of  lime  rock  and  tvould  like  to  know  whether  it 
would  be  practical  to  mine  it  and  mix  it  with  our  surface 
clay.  We  have  tested  this  shale  in  various  u>ays  and  find  that 
it  will  add  to  the  quality  of  our  ware  and  «'///  aid  in  the  dry- 
ing without  cracking. 

The  fact  that  your  shale  is  overlaid  by  a  stratum  of 
limestone  would  be  a  big  point  in  favor  of  mining  it.  An 
expensive  factor  in  mining  operations  is  the  cost  of 


CLAYWORKING  PROBLEMS 


timbering  the  roof  in  order  to  make  the  mine  a  safe  place 
in  which  to  work,  and  also  to  conform  to  the  laws  gov- 
erning mine  working.  The  limestone  roof,  in  many  cases, 
does  away  entirely  with  timbering,  thus  decreasing  the 
cost  of  operating  the  mine. 

Mining  is  certainly  more  expensive  than  gathering 
surface  clay,  and  this  point  must  be  considered  in  de- 
ciding to  use  your  shale.  You  must  determine  whether 
or  not  the  addition  of  the  shale  to  your  surface  clay 
will  increase  the  value  and  sale  of  the  finished  product. 
If  you  can  get  a  better  price  for  your  ware  by  the  ad- 
dition of  the  shale  and  be  able  to  sell  more  of  it  at  a 
margin  that  will  pay  for  the  added  cost  of  mining  and 
still  leave  you  a  little  profit,  we  should  say  that  it  would 
be  a  good  proposition  for  you  to  use  your  shale. 

Your  first  step,  it  seems  to  us.  is  to  determine  the  cost 
of  opening  a  new  mine  and  the  tonnage  cost  of  mining 
in  your  particular  case.  This  could  best  be  solved  by 
submitting  your  problem  to  a  reliable  mining  engineer, 
who  could  tell  you  how  much  it  is  going  to  cost  yon  per  ton 
to  mine  vour  shale. 


Thinks  Slate  Will  Make  Brick. 

638.  Arizona — Some  friends  of  mine  are  interested  in  a 
slate  deposit  near  here  and  a  recent  analysis  shows  the  fol- 
lowing : 

Aluminum    (A1203)   22.4  c/f 

Silica    ( SiOo)    65.8  % 

Iron     (FeO)     5.58% 

Magnesia    (MgO)    1.8  % 

95.58% 

This  slate  is  such  that  it  cleaves  well  and  if  the  quality  is 
all  right  it  ran  be  handled  so  far  as  working  it  is  concerned. 


CLAYWORK1NG  PROBLEMS  151 

Do  you  think  from  this  analysis  that  it  would  make  a  good 
quality  of  pressed  brick? 

There  is  no  way  in  which  we  can  predict  the  action  of  a 
mineral  from  chemical  analysis. 

We  may  hazard  a  guess  and  in  this  instance  our  guess  is 
that  the  silica  is  too  high,  the  alumina  too  low  and — this  is 
no  guess — the  working  qualities  of  slate  or  metamorphosed 
shale  are  zero. 

There  are  slates  and  other  minerals  that,  seemingly,  have 
the  same  chemical  composition  as  clays  that  have  proved  use- 
ful while  at  the  same  time,  the  physical  nature  of  these 
slates  has  destroyed  the  value  from  a  clayworking  standpoint. 


Will  Motor  Loads  on  Same  Shaft  Vary? 

617.  North  Dakota— If  two  motors  having  the  same  speed 
and  same  sice  pulleys  should  be  connected  up  to  drive  a  ma- 
chine as  shown  in  the  accompanying  sketch,  ivill  there  be  any 


difference  in  the  load  of  the  motors  provided  there  is  abso- 
lutely no  slippage  in  the  belts,  or  will  motor  pulleys  have  to 
be  slightly  different  in  diameter  as  in  the  ordinary  tandem 
drive  to  give  motors  an  equal  load? 

Provided  the  two  motors  in  question  have  the  same  gen- 
eral characteristics,  the   same  capacity  and  speeds,  the  load 


152  CLAYWORKING  PROBLEMS 

would  divide  equally  between  them.  The  pulleys  to  do  this 
would  have  to  be  of  the  same  size. 

If  two  motors  of  different  horsepower  rating  are  used,  the 
tendency  would  be  to  put  a  slightly  greater  load  on  the  large 
motor,  assuming  that  the  speeds  were  the  same.  The  rea- 
son for  this  is  due  to  the  fact  that  the  variation  in  speed  from 
no  load  to  full  load  is  slightly  less  on  a  large  motor  than  it 
is  on  a  small  motor,  as  motors  are  commercially  made. 

This  variation  could  probably  be  overcome  by  placing  the 
large  motor  inside,  that  is,  between  the  motor  with  two  belts 
and  the  driving  shaft,  and  vary  the  load  on  this  slightly  by 
belt  adjustment. 

Motors  of  different  capacities  with  exactly  the  same  char- 
acteristics would  divide  the  load  in  proportion  to  the  ratings 
of  the  motor  when  all  question  of  belt  slippage  is  eliminated. 
In  other  words,  for  a  thirty  horsepower  load  using  a  twenty 
and  ten  horsepower  motor,  each  motor  would  be  running  at 
full  load,  or  practically  so. 


Wants  to  Glaze  Under  Side  of  Kiln  Crown. 

623.  Indiana — Please  let  us  hare  your  best  method  of  glaz- 
ing the  under  side  of  a  kiln  crown  made  of  red  brick.  Ours 
is  a  round  down-draft  kiln  and  we  burn  at  about  2.000  de- 
grees Fah.  at  the  crown. 

Make  up  a  daub  of  fire  clay  and  salt,  the  proportion  being 
about  one  iron  wheelbarrow  load  of  the  clay  to  one-half  of 
one  shovel  full  of  salt.  Mix  with  water  to  the  consistency 
of  paint  and  daub  over  the  under  side  of  the  crown  with  a 
stiff  broom.  Try  the  above  proportions  first  on  a  small  patch, 
for  if  it  contains  too  much  salt  it  will  blister  during  the 
glazing.  If  it  does  not  glaze  at  all,  double  the  quantity  of 
salt  which  goes  into  the  next  batch  and  keep  on  adding  at 
the  rate  of  one-half  a  shovelful  of  salt  to  a  wheelbarrow- 
load  of  clay,  until  the  correct  proportions  are  ascertained. 


CLAYWORKING  PROBLEMS  153 

It  is  impossible  to  give  you  a  correct  mixture,  inasmuch  as 
the  alumina-iron  content  of  the  brick  in  the  crown  bears  a 
definite  ratio  to  the  fluxing  or  melting  point  of  the  body 
silicate.  The  salt  tends  to  reduce  the  fluxing  point  and  the 
amount  of  salt  added  has,  therefore,  a  definite  work  to  do. 
Too  much  causes  a  pimpled,  viscous  structure  and  not  enough 
causes  no  reaction  and,  therefore,  no  glazing. 

The  same  glaze  effect  may  be  obtained  by  throwing  four 
shovelfulls  of  salt  in  the  furnace  at  two  or  three  hour  in- 
tervals during  the  last  six  or  eight  hours  of  burning.  In 
addition  to  glazing  the  crown,  this  will  also  glaze  the  ware 
in  the  kiln,  and  if  glazed  ware  is  not  desirable,  the  method 
first  described  should  be  adopted. 


Analysis  in  Sand-Lime  Brick  Manufacture 

680.  Quebec — We  manufacture  a  sand-lime  brick,  and  as 
I  found  it  advisable  to  analyse  the  mixture  during  the  process 
of  manufacture  and  also  to  analyse  the  finished  brick  for  the 
calcium  content,  I  shall  be  glad  if  you  will  g'vve  me  a  few 
pointers  on  the  subject  or  refer  me  to  the  suitable  text  books. 
I  may  say  that  I  have  Treadwell's  "Analytical  Chemistry" 
but  the  process  therein  described  appears  to  me  to  be  more 
suitable  for  the  laboratory  than  for  a  factory.  I  presume 
that  the  process  to  be  continuous  should  be  that  of  titration 
as  precipitation  is  much  too  slow  a  system.  I  should  like  also 
to  be  in  a  position  to  analyse  the  lime  (CoO)  for  CaCo*  from 
time  to  time  as  deemed  advisable.  I  want  to  know  just  how 
to  make  up  my  normal  solutions  of  hydrochloric  acid  (HCl) 
and  sodium  hydrate  (NaOH)  and  the  method  of  calculating 
the  percentage  of  the  carbonate  and  oxide  after  titration. 
This  would  be  very  valuable  information  both  to  myself  and, 
no  doubt,  many  of  your  readers;  any  light  on  the  subject 
would  be  heartily  welcomed. 

E.  T.  Montgomery,  E.  M.  in  Cer.,  of  Alfred,  N.  Y.,  says 
that  the  best  method  for  the  rapid  determination  of  calcium 


CLAYWORKING  PROBLEMS 


bv  titration  process  is  that  which  is  given  on  pages  22  and 
23  and  following  of  "Notes  on  Metallurgical  Analysis,"  by 
N.  W.  Lord,  formerly  Professor  of  Metallurgy  at  the  Ohio 
State  University.  He  suggests  that  our  correspondent  will 
have  no  difficulty  in  securing  this  text,  although  it  was  writ- 
ten in  1903.  Hann  and  Adair,  of  Columbus,  Ohio,  are  the 
publishers  and  printers. 

For  the  examination  of  the  lime.  Professor  Montgomery 
suggests  the  use  of  Schroetter's  Alkalimeter  which  is  cata- 
logued by  Eimer  &  Amend,  of  New  York  City,  as  Alkali- 
meter  No.  1752.  Eimer  &  Amend  should  be  able  to  give  a 
description  of  the  use  of  this  Alkalimeter  or  give  a  reference 
to  some  text  book  which  discusses  its  use,  but  if  our  corre- 
spondent finds  it  impossible  to  obtain  anything  of  this  kind, 
Professor  Montgomery  states  that  he  will  be  willing  to  give 
him  a  detailed  statement  relative  thereto. 

We  are,  of  course,  assuming  that  in  our  correspondent's 
examination  of  the  lime  which  he  is  buying  as  one  of  the 
raw  materials,  he  desires  to  ascertain  only  the  CO2  content 
which  is,  of  course,  the  measure  of  the  amount  of  either 
CaCo-  or  MgCO3  present. 

As  far  as  determining  the  calcium  content  of  the  mortar 
or  raw  mix  is  concerned,  it  would  seem  that  the  examination 
of  the  lime  would  be  sufficient  unless  our  correspondent  is 
seeking  to  ascertain  whether  a'.l  of  the  CaO  in  the  mortar 
has  been  completely  hydrated.  In  the  second  place,  the  cal- 
cium in  his  finished  product  exists  in  three  different  forms 
— that  of  calcium  silicates,  some  calcium  carbonate  and  some 
uncombined  calcium  hydrate.  We  do  not  understand  where 
he  will  derive  any  benefit  from  determining  the  total  calcium 
in  the  finished  product  as  the  amount  which  has  entered  into 
combination  as  a  silicate  is  a  measure  of  the  efficiency  of  his 
hardening  process. 

Technologic  Paper  No.  16  by  W.  E.  Emley  from  the 
U.  S.  Bureau  of  Standards  at  Washington,  D.  C,  will  prove 
of  value  to  this  correspondent  as  will  also  Bulletin  No.  18 


CLAYVVORKING  PROBLEMS  155 

on  "Sand-Lime  Brick"  from  the  Geological  Survey  of  Illinois 
at  Urbana,  111. 


Comparative  Cost  of  Coal  and  Oil  Fuel 
683.  South  Dakota — Where  can  I  get  the  best  information 
relative  to  the  cost  of  burning  oil  in  place  of  coal  for  brick 
and  building  blocks?  I  want  to  know  the  cost  per  M.  of 
burning  petroleum  tailings  as  compared  to  the  cost  of  coal  at 
$4.00  per  ton. 

We  are  advised  by  an  authority  on  the  subject  of  oil  that  it 
is  good  practice  to  figure  126  gallons  of  fuel-oil  as  being  equal 
to  a  ton  of  average  quality  coal.  Fuel-oil  costs  about  1^4 
cents  per  gallon  at  the  refinery  and  as  the  freight  rate  from 
the  nearest  refinery  to  your  plant  would  be  between  forty 
and  forty-five  cents  per  cwt.  this  would  make  the  fuel  oil 
cost  you  something  like  4^4  cents  per  gallon.  At  this  rate 
126  gallons  of  oil  would  cost  you  about  $6.  Coal  at  $4  per 
ton  would  be  very  much  cheaper.  We  note  your  use  of  the 
term  "petroleum  tailings"  and  wish  to  explain  that  this  is 
only  another  name  for  fuel-oil.  It  was,  we  understand,  used 
by  some  Oklahoma  refineries  for  the  purpose  of  securing  a 
better  freight  rate  than  was  given  fuel-oil,  but  the  Interstate 
Commerce  Commission  has  ruled  against  this  lower  rate  and 
Oklahoma  "petroleum  tailings"  are  again  fuel-oil — as  they 
always  were  in  everything  but  name. 


The  Manufacture  of  Silica  Brick 

685.  Pennsylvania — Will  you  please  tell  me  where  I  could 
get  a  book  about  lime-bond  silica  brick — about  making  and 
burning  it? 

T.  E.  Montgomery,  E.  M.  (in  Cer.)  of  Alfred,  New  York, 
in  an  article  published  in  "Brick  and  Clay  Record,"  in  May, 
1914,  has  this  to  say  about  the  manufacture  of  silica  brick: 

In  the  development  of  the  siliceous  refractories  indus- 


CLAYWORKING  PROBLEMS 


try,  an  unfortunate  confusion  of  names  has  arisen.  This 
is  partly  due  to  the  fact  that  from  the  beginning  of  the 
industry  two  different  binding  materials  have  been  used, 
viz.:  lime  and  fire  clay.  The  name  "Dinas"  was  first  used 
in  the  beginning  of  the  19th  century  by  a  Mr.  Weston 
Young,  who  worked  the  siliceous  materials  of  the  Di- 
nasfels  of  Wales  into  brick,  using  as  a  bond  the  underly- 
ing cretaceous  lime.  This  process  was  kept  a  secret  by 
the  Young  family  until  the  middle  of  the  century,  and  in 
the  meantime  another  siliceous  brick  was  put  on  the  mar- 
ket in  England,  which  was  made  by  grinding  and  mixing 
the  gannister  rock  of  Sheffield  with  fire  clay.  This  was 
called  "Gannister"  brick,  and  the  name  is  still  generally 
applied  in  England  to  such  siliceous  brick  bonded  with 
clay.  The  Germans  soon  began  the  manufacture  of  a  clay 
bonded  silica  brick  and  called  it  "German  Dinas,"  so  we 
have  in  Europe  the  term  "Dinas"  applied  to  both  lime  and 
clay  bonded  silica  brick.  In  this  country  we  have  never 
used  the  term  Dinas.  High  grade  silica  brick  bonded  with 
lime  are  called  "Silica,"  and  the  term  "Quartzite"  and 
"Gannister"  have  been  applied  to  different  grades  of  clay 
bonded  brick. 

In  the  manufacture  of  silica  brick  the  best  results  have 
been  obtained  in  the  use  of  sedimentary  sandstones  and 
quartzites  containing  about  97  per  cent  of  silica  and  3  per 
cent  of  impurities.  In  the  west,  however,  in  Montana  and 
Utah,  crystalline  quartz  rocks  are  used.  Attempts  to  use 
a  too  pure  quartzite — 99  per  cent  SiC>2 — have  not  been 
successful.  There  is  only  one  property  or  quality  of  major 
importance  in  selecting  a  material  for  the  manufacture  of 
silica  brick,  while  there  are  two  or  three  other  minor  ones. 
It  must  be  remembered  that  silica  brick  expand  on  being 
burned  in  the  process  of  manufacture,  and  are  fired  up  to 
dimensions  instead  of  shrinking  to  dimensions,  as  in  the 
case  of  fire  clay  brick.  It  has  been  shown  in  testing  dif- 


CLAYWORKING  PROBLEMS  157 

ferent  quartzites  that  they  vary  from  3.2  per  cent  to  23.5 
per  cent  in  volume  increase  in  the  first  burn.  The  lowest 
figure  of  3.2  per  cent  is  for  a  very  pure  quartz,  coarsely 
crystalline,  which  disintegrates  to  a  fine  powder  on  burn- 
ing. The  Higher  value  of  23.5  per  cent  was  for  fine  grained, 
hard,  tough  quartzites  with  about  3  per  cent  impurities 
and  which  remained  firm  and  hard  after  burning.  It  is 
obvious  that  we  want  a  material  which  does  practically  all 
of  its  expanding  in  the  burning  it  gets  before  put  into  use. 
These  quartzites  which  have  a  low  volume  increase  in  the 
first  burn,  change  in  volume  slowly  and  continuously  over 
a  long  period,  and  hence  swell  after  being  put  in  place  in 
actual  use. 

The  physical  condition  of  the  crushed  material  is  also 
of  importance.  Round  grained  sand  cannot  be  used,  as 
it  will  not  bond  properly.  Even  sharp  grained  sand  is  not 
good,  because  the  size  of  grain  is  too  uniform.  A  rock 
which  grinds  to  splinters  and  particles  of  irregular  size, 
which  overlap  and  interlock,  makes  a  brick  of  the  best 
structure. 

According  to  the  kind  of  brick  being  made,  there  is 
added  to  the  crushed  rock  in  making  the  mix,  either  2  per 
cent  of  slaked  lime  or  from  20  to  30  per  cent  of  fire-clay. 
The  batch  is  ground  and  tempered  in  a  wet  pan  and  then 
molded  by  hand  in  a  brick  mold  by  what  is  called  the 
"slop  molding"  process,  the  excess  material  being  cut  off 
at  the  top  of  the  mold  by  a  scraper.  The  brick  are  then 
dried  on  a  drying  floor  or  rack  until  they  are  hard  to 
dent  with  the  finger,  when  they  are  repressed.  After  the 
brick  are  thoroughly  dried  they  are  set  in  the  kilns  and 
fired  to  temperatures  varying  all  the  way  from  cone  9  to 
cone  18  in  different  plants.  The  temperature  used  depends 
on  that  required  by  the  material  to  properly  develop  the 
bond  and  to  secure  the  necessary  volume  increase,  i.  e., 


158  CLAYWORKING  PROBLEMS 

to  bring  the  volume  changes  as  near  as  possible  to  a  con- 
dition of  equilibrium. 

Silica  brick  are  chemically  acid  and  are  used  not  only  in 
positions  where  an  acid  brick  is  necessary,  but  are  yearly 
finding  many  other  uses  due  to  their  high  refractoriness, 
regular  expansion  and  heat  diffusivity  and  ability  to  carry 
loads  at  high  temperatures  without  deformation  as  long 
as  these  temperatures  are  at  a  safe  interval  below  their 
melting  point.  Silica  brick  are  used  in  connection  with 
silica  sand  mass  in  acid  open-hearth  furnaces;  they  are 
largely  used  in  crowns  of  by-product  and  bee-hive  coke 
ovens;  in  the  glass,  iron  and  copper  melting  business;  and 
in  some  places  for  boiler  settings  and  fire  box  linings. 

As  we  would  expect  from  our  knowledge  of  calcium 
silicates,  silica  brick  have  been  found  to  have  a  well  de- 
fined melting  point.  There  is  practically  no  softening 
or  flow  until  the  melting  point  has  been  reached,  when  it 
will  suddenly  fuse  to  a  liquid  of  low  viscosity.  Mr.  George 
Brown  in  load  tests  on  silica  brick  made  in  the  Bureau 
of  Standards  laboratory,  has  shown  that  they  are  not  af- 
fected by  the  usual  test  of  50  pounds  per  square  inch  at 
1,350  degs.  C,  nor  even  when  the  temperature  was  car- 
ried as  high  as  1,470  degs.  C.  This  test  was  on  a  silica 
brick  with  lime  binder. 

A  silica  brick  with  clay  binder  showed  a  small  de- 
flection under  load  of  50  Ibs.  at  1,350  degs.  Silica 
brick  fuse  or  melt  at  about  a  temperature  of  1,750 
degs.  C. 


Preheating  a  Plastic  Clay 

430.  West  Virginia — /  hare  a  sample  of  clay  before  me 
which  has  baffled  me,  H/>  to  this  time,  and  will  ask  yoiw  as- 
sistance. It  is  rery  plastic  clay  and  resembles  Tennessee  ball 
clay  in  color  and  strength.  It  acts  rery  differently,  however, 
in  drying,  cracking  all  over  the  surface  and  is  rery  tender 


CLAYWORKIXG  PROBLEMS 


when  thoroughly  dry.  The  shrinkage  is  about  seven  per  cent. 
I  can  stop  the  cracking  by  adding  about  twenty  per  cent 
Tennessee  ball  clay,  but  do  not  wish  to  adulterate,  as  this 
lowers  its  fusing  point,  which  is  about  4,000  degress  F.  Can 
you  suggest  a  method  of  working  this  clay  and  avoiding  the 
cracking?  I  hare  aged  the  clay  for  several  months  and  have 
tried  casting,  pressing  and  throwing,  with  no  results.  Have 
added  flint  and  grog  to  open  the  clay,  and  with  no  results. 
As  I  have  said,  I  can  cure  this  fault  by  adding  ball  clay,  and 
still  have  a  splendid  refractory  clay,  but  I  am  not  willing  to 
do  this  until  I  am  sure  that  there  is  no  other  way. 

Professor  Bleininger,  of  the  U.  S.  Bureau  of  Standards,  has 
shown  that  the  drying  behavior  of  excessively  plastic  clays 
can  be  improved  in  a  decided  manner  by  preheating  them 
to  temperatures  of  from  200  degrees  to  400  degrees  C,  the 
intensity  of  the  heat  treatment  depending  upon  the  clay  in 
question.  The  results  of  this  work  showed  that; 

1.  Preheating   seems   to   convert   part   of   the   plastic   clay 
substance  into  a  modification  which  can  not  be  made  plastic 
again.      Such    clays    dry   more   easily,    due   principally   to   in- 
creased porosity. 

2.  The  preheating  should  be  carried  on  at  as  low  a  tem- 
perature as  possible,  only  high  enough  to  overcome  the  dry- 
ing difficulty.     High  temperatures  with  some  clays  result  in 
excessive  pore  space  which  may  give  rise  to  burning  difficul- 
ties due  to  cracking.     It  is  quite  likely  that  some  clays  cannot 
be  preheated  at  all  owing  to  the  short  temperature  range  with- 
in which  the  change  takes  place.    It  is  impossible  to  give  gen- 
eral rules ;  each  clay  must  be  studied  by  itself. 

3.  Most  clays  seem  to  require  more  careful  lubrication  in 
the    preheated    than    in    the    normal    state.     The   amount    of 
tempering  water  should  be  kept  as  low  as  possible. 

4.  There  seems  to  be  a  tendency  on  the  part  of  the  pre- 
heated clay  to  release  its  soluble  salts  more  readily  than  nor- 


CLAYWORKING  PROBLEMS 


mal  clay;  this  would  indicate  a  greater  tendency  to  show 
dryer  efflorescence. 

Depending  on  the  amount  of  clay,  the  time  required  varies 
from  3  to  5  hours.  The  rotary  dryer  seems  to  be  the  most 
suitable  apparatus  for  this  paper. 

A  more  detailed  description  of  this  investigation  can  be 
found  in  "Bulletin  No.  I— Technologic  Papers  of  the  Bureau 
of  Standards."  It  can  be  obtained  free  of  cost  by  address- 
ing The  Director,  Bureau  of  Standards,  Washington,  D.  C. 


Improperly  Tempered  Clay  Causes  Drying  Losses 

578.  Indiana — For  the  last  ten  years  I  hare  operated  a  small 
yard  during  the  summer  season  manufacturing  brick,  but 
due  to  the  demand  for  drain  tile,  I  bought  a  complete  second- 
hand outfit  of  stiff-mud  machinery  last  summer  to  supple- 
ment the  existing  equipment.  This  outfit  included  a  pug  mill, 
auger  machine  and  automatic  cutter.  The  outfit  works  very 
well,  but  my  drying  loss  is  enormous,  sometimes  losing  forty 
per  cent  of  a  day's  run.  I  am  certain  of  this  point,  at  least, 
my  w'arc  is  not  tempered  evenly;  some  of  it  comes  so  wet 
that  it  is  difficult  to  handle  and  the  next  batch  is  dry  and 
hard.  I  have  placed  the  best  man  I  have  available  on  the 
pug  mill  but  results  are  but  little  better  than  before.  Do 
you  know  of  any  scheme  that  will  help  the  pugger  to  main- 
tain an  evenly  tempered  batch  of  clay  all  of  the  time? 

From  the  data  available  in  your  inquiry,  it  appears  that 
the  pugger  not  only  operates  the  flow  of  the  water,  but  also 
the  flow  of  clay.  He  has  two  varying  quantities  to  deal  with; 
he  regulates  the  flow  of  clay  to  agree  with  the  output  of 
ware,  endeavoring  to  secure  an  even  flow.  He  has  the  tem- 
per water  to  regulate  to  suit  the  amount  of  clay  in  the  mill 
and  also  has  to  watch  the  condition  of  the  ground  clay  ad- 
mitted to  the  mill,  with  its  variation  in  water  content. 

To  eliminate  one-half  of  the  difficulty,  we  recommend  the 


CLAYWORKING  PROBLEMS  161 


securing  of  a  clay  feeder.  By  its  use,  the  clay  flow  is  regu- 
lated to  suit  the  output,  permitting  the  pugger  to  give  his 
entire  attention  to  the  "feel"  of  the  mud. 


Brick  Crack  in  Drying 

601.  New  York — /  am  sending  you  by  parcel  post  a  small 
quantity  of  our  shale,  taken  from  a  pit  that  -we  have  recently 
opened.  This  sample  was  taken  after  it  had  passed  the  screen. 
I  am  sending  it  to  you  in  hope  that  you  will  be  able  to  find 
out  n'hy  it  is  that,  in  making  standard  sice  brick,  it  is  ex- 
tremely fragile.  The  brick  crack  in  the  dryer  and  even  show 
signs  of  fracture  when  they  stand  in  the  air,  if  the  car  is  al- 
lowed to  wait  its  turn  into  the  tunnels.  We  are  using  a  home- 
made, wooden  pug-mill,  about  seven  feet  long,  feeding  into 
an  auger  machine.  The  brick  look  fine  when  first  cut,  but 
are  rery  fragile. 

After  examining  the  sample,  we  are  convinced  that  the 
trouble  lies  mainly  in  the  clay's  being  ground  too  coarsely. 
The  particles  are  large  and  the  tendency  to  bond  and  be- 
come plastic  enough  for  suitable  working  qualities  is  weak. 
This  can  be  remedied  in  part  by  the  installation  of  a  screen 
that  will  reject  the  coarser  particles,  supplemented  by  screen 
plates  in  the  dry-pan  that  are  finer  than  those  you  now  use. 
We  also  suggest  that  the  pug-mill  be  lengthened  to  ten  or 
twelve  feet  and  that  it  be  equipped  with  a  feeder.  Try  hot 
water  for  tempering. 


This  Dryer  Does  Not  Dry 

619.  Pennsylvania — We  would  like  to  have  some  advice 
about  our  dryer.  We  are  making  a  soft-mud  brick,  six  in  a 
mold,  placed  on  a  wooden  pallet,  414  brick  to  a  car,  the  pal- 
lets being  spaced  three  inches  apart  on  the  cars.  The  dryer 
holds  33.000  brick;  we  set  11,000  in  the  morning  and  make 
11,000  in  the  afternoon,  draiving  the  cars  as  the  new  ones 


CLAYWORKING  PROBLEMS 


are  put  in — this  is,  at  the  end  of  three  days.  Our  trouble  is 
that  the  brick  are  not  always  dry  at  the  end  of  three  days, 
but  we  hare  to  draw  them,  or  stop  making  brick.  The  dryer 
is  a  home-made  affair,  75  by  40  feet  outside  measurement. 
The  outside  w'alls  are  of  brick,  as  well  as  a  nine-inch  wall 
that  divides  the  dryer  into  tw'o  chambers.  The  roof  is  about 
5:/2  feet  aborc  the  tracks  and  is  double  boarded.  On  it  we 
have  about  ten  inches  of  clay,  ivith  a  double  pitch  roof  above 
this.  We  hare  eight  tracks,  holding  ten  cars  each,  the  ground 
being  even  with  the  tics,  and  our  steam  pipe  is  all  between  the 
tracks — on  the  tics.  There  is  10,000  //.  of  steam  pipe  in  all 
— sixteen  lengths  by  full  length  of  the  dryer.  The  diameter 
of  the  pipe  is  one  inch. 

We  have  twelve  ventilators  up  through  the  roof,  that  are 
ten  inches  square,  and  two  stacks  16  by  38  in.  and  24  ft.  high. 
There  are  two  sets  of  doors  at  the  stack  end  of  the  dryer, 
the  bottom  of  the  inside  doors  being  ten  inches  above  the 
tracks.  Our  idea  is  to  drazv  the  vapor  down,  under  this  door, 
and  up  through  flic  stack.  At  the  other  end  of  the  dryer, 
we  have  a  cold  air  flue  eighteen  inches  square,  the  full  width 
of  the  dryer — which  is  40  ft. — with  a  ten-inch  opening  under 
each  track,  extending  ten  feet  inside  of  the  dryer,  to  help  drive 
off  tlie  vapor.  For  steam,  zvc  have  two  50-h.p.  boilers,  carry- 
ing 80  Ibs.  pressure,  day  and  night. 

Theoretically,  there  is  no  reason  why  this  dryer  should  not 
dry  33,000  brick  in  three  days.  Practically,  according  to  our 
questioner,  it  fails.  Since  the  theory  is  correct  and  the  prac- 
tice wrong,  there  is  no  way  of  solving  the  trouble  at  a  dis- 
tance. \Ye  would  strongly  urge  the  questioner  to  send  for 
a  brickworks'  engineer — one  who  makes  a  specialty  of  dryers 
— paying  a  fee  for  his  advice,  but  insisting  that  the  advice 
be  given  after  a  personal  inspection  of  the  dryer. 


To  Cure  Blisters  on  Drain  Tile. 

606.     Illinois — ll'c  are  having  a  great  deal  of  trouble  mak- 
ing our  large  sice  drain  tile,  especially  the  fifteen  inch.    They 


CLAYWQRKING  PROBLEMS  163 

run  fairly  well  at  the  machine  and  do  not  show  up  any  great 
loss  in  drying.  They  seem  to  be  in  first-class  condition  when 
set  in  the  kiln,  but  when  we  open  the  kiln  sometimes  half 
or  more  of  our  large  tile  are  spoiled  entirely.  They  seem 
to  blister  or  blow  out  in  patches  of  from  four  to  sixteen 
inches  in  diameter.  Sometimes  we  have  very  little  loss  and 
yet  so  far  as  we  can  see,  our  clay,  machinery  and  general 
process  of  manufacture  are  identical  with  the  conditions  that 
existed  before  these  losses  began  to  occur.  We  have  lately 
found  that  some  of  our  tile  when  dry,  show  blisters  which 
are  about  a  half-inch  high  and  possibly  six  inches  in  diame- 
ter. When  we  break  these  open  we  find  the  surface  of  the 
clay  somewhat  polished,  just  as  if  there  had  been  laminations 
which  were  not  knitted  together.  If  you  or  any  of  your 
readers  can  gire  us  any  pointers,  we  will  appreciate  it,  and 
if  you  want  any  more  information  we  will  be  glad  to  give  it 
to  you  or  them. 

We  are  inclined  to  think  that  the  difficulty  lies  either  in 
unevenly  ground  clay  or  in  unevenly  tempered  clay.  Unless 
you  have  already  taken  every  precaution  to  insure  an  un- 
varying supply  of  uniformly  ground  clay  coming  to  the  pug 
mill  and  there  being  mixed  with  an  unvarying  quantity  of 
water,  this  is  the  most  likely  place  to  look  for  the  solution 
of  your  blistering  problem.  If,  on  the  other  hand,  you  have 
taken  every  precaution  along  this  line,  and  the  trouble  which 
you  report,  continues  to  exist,  then  there  is  a  possibility  that 
your  clay  is  not  sufficiently  tempered  or  that  it  is  forced  into 
the  auger  or  plunger  in  too  dry  a  condition,  and  that  lamina- 
tion is  set  up  by  friction  in  passing  through  the  die.  This 
is  a  very  common  cause  of  "bubbles"  or  "shelling."  The 
reason  is  obviously  a  differential  flow  of  clay  through  the  die 
under  high  pressure — not  sufficient  lubrication  or  too  much 
friction.  Also  if  the  clay  is  not  tempered  thoroughly,  it 
cannot  knit  together  the  smooth  surfaces  that  are  caused 
by  the  action  of  the  auger,  and  these  surfaces  do  not  bond 


164  CLAYWORKING  PROBLEMS 

together  sufficiently  to  resist  dry  shrinkage.  It  might  be  well 
also  for  you  to  look  at  your  auger  and  see  whether  or  not 
it  is  very  much  worn.  A  worn  auger  is  a  common  cause  of 
the  difficulty  which  you  have  mentioned,  although  it  is  sel- 
dom given  the  proper  consideration.  Look  into  this  part 
of  your  manufacture — from  the  point  where  you  grind  your 
clay  to  the  point  where  the  clay  leaves  the  die  and  see  if  you 
cannot  find  a  remedy  there,  before  going  any  farther.  Trou- 
ble may,  of  course,  be  in  the  dryer  but  we  are  inclined  to 
think  that  it  lies  earlier  in  your  process. 

The  above  question  was  published  in  the  Jan.  5th  issue  and 
an  answer  given  which  has  brought  forth  some  criticism.  Ed 
C.  Mead  of  the  Enfield  Vitrified  Brick  &  Tile  Company  of 
Enfield,  111.,  writes  us  as  follows: 

"I  want  to  criticise  the  reply  to  question  No.  606  in  'Brick 
and  Clay  Record'  of  Jan.  5th  issue,  in  regard  to  blisters  on 
drain  tile.  This  is  one  trouble  I  learned  to  eliminate  before  I 
was  large  enough  to  do  any  firing,  except  slow  firing.  It  is 
also  a  trouble  encountered  on  a  great  many  yards,  and  as  a 
rule,  with  a  little  thought  a  speedy  remedy  is  found. 

"To  me  it  is  absurd  to  connect  the  auger  lamination  with 
this  trouble  in  hollow  ware,  nevertheless,  it  is  true,  this 
trouble  is  met  with  most  frequently  in  the  more  plastic 
material.  Lamination  in  drain  tile  is  of  little  consequence 
when  the  ware  is  dried  and  burned  properly  according  to 
circumstances,  and  is  caused  by  the  friction,  'on  both  ring 
and  core  of  die,'  of  material,  allowing  the  center  of  wall 
to  travel  more  freely  and  naturally  faster.  It  is  easily  under- 
stood how  this  condition  will  break  the  bond  and  leave  lam- 
inations extending  lengthwise  and  around  the  circle,  and  in 
some  cases  almost  unbroken  during  any  continuous  operation 
of  machine.  Under  the  same  conditions  a  plunger  machine 
will  produce  the  same  results  as  the  auger  method.  To  elim- 
inate the  blisters  'if  noticeable  in  dried  ware'  dry  slower  in 


CLAYWORKING  PROBLEMS  165 

the  early  stages  and  if  ware  goes  into  kiln  sound  and  then 
blisters,  the  cure  would  be  to  fire  with  less  speed,  being 
sure  to  maintain  .an  even  and  gradual  increase  in  temperature. 
If  you  will  furnish  me  the  address  of  the  brother  claycrafter 
I  will  gladly  furnish  him  the  results  of  my  experience  after 
ascertaining  more  fully  the  conditions. '  My  motto  is :  'Help 
those  in  trouble.  Boost  clay  products.' " 


To  Prevent  Slipping  of  Clay  Bar 

579.  Ohio — I  am  making  a  partition  tile  3x12x12  inches 
in  sice.  The  clay  column  as  it  comes  from  the  die  has  not 
the  weight  to  give  a  steady  push  to  the  cutter  and,  there- 
fore, the  wires  will  not  make  a  vertical  cut  but  tear  through 
diagonally,  sometimes  causing  the  bar  of  clay  to  crumple  up 
entirely.  I  hare  roughened  the  boards  and  have  covered  the 
same  with  course  canvas,  but  in  every  case,  each  attempt  has 
helped,  but  only  temporarily.  As  soon  as  the  boards  get  wet, 
the  slipping  starts  again  in  spite  of.  my  efforts.  What  do 
you  think  is  the  real  trouble  and  how  can  we  remedy  itf 

There  are  several  serious  faults  which  may  be  the  cause 
of  your  trouble.  The  die  lubrication  may  be  excessive,  caus- 
ing a  thin,  slushy  surface  to  appear  on  the  column.  This 
should  be  watched,  and  if  you  find  it  the  case,  this  condition 
can  easily  be  stopped  by  the  adjustment  of  the  lubricating 
device  on  your  die. 

Perhaps  the  boards  from  the  pug  mill  to  the  cutter  may 
not  be  wide  enough  to  give  all  possible  grip  to  the  bar  of 
clay.  This  also  can  easily  be  remedied.  The  reel  may  be  turn- 
ing stiffly.  If  so,  loosen  the  set  screws  in  the  uprights. 

The  bar  of  clay  may  be  running  down  hill.  This  we  be- 
lieve to  be  the  most  probable  cause  of  your  difficulty.  In 
this  case,  adjust  the  cutter  so  that  the  receiving  end  is  about 
one-eighth  to  one-quarter  of  an  inch  below  the  bottom  of 


166  CLAYWORKING  PROBLEMS 

the  lower  side  of  the  die,  then  raise  the  discharge  end  of 
the  cutter  so  that  it  is  from  one-half  to  two  inches  higher 
than  the  receiving  end.  This  causes  the  clay  to  flow  uphill 
and  the  friction  is,  therefore,  increased. 

Since  publishing  the  above,  we  have  received  the  following 
from  James  J.  Hinde,  of  the  Hinde  Brick  and  Tile  Company, 
of  Sandusky,  Ohio,  who  says:  "A  better  remedy  is  to  assist 
driving  the  cutting  table  with  a  small  friction  belt  or  sprocket 
chain  which  can  be  driven  from  the  auger  mill. 


The  Effect  of  Artificial  Drying  on  Clay 

ITS.  NCI*.'  Jersey — ll'HI  you  kindly  let  me  know  what  effect 
as  to  strength  and  quality  artificial  drying  has  on  clay,  li'hen 
dried  at  a  temperature  of  140  to  180  degrees  F.f 

Ellis  Lovejoy,  answering  the  above  question,  says;  "It 
depends  entire!y  upon  the  character  of  the  clay.  Some  clays 
can  be  put  into  dryers  and  immediately  subjected  to  tem- 
peratures much  higher  than  180  degrees,  without  in  any  way 
affecting  the  strength  and  quality,  but  there  are  other  clays 
which  are  so  tender  in  their  drying  behavior,  that  the  lower 
temperature  mentioned  (140  degrees  F.)  would  cause  exces- 
sive loss.  The  effect  upon  ware  depends  upon  two  factors. 
First,  the  date  of  evaporation  from  the  surface  of  the  ware; 
second,  the  rate  at  which  the  water  within  the  ware  comes 
to  the  surface.  Whenever  the  rate  of  evaporation  is  greater 
than  the  rate  at  which  the  water  is  brought  to  the  surface 
by  capillarity,  the  ware  invariably  cracks.  When  the  rate 
of  evaporation  equals  the  rate  of  capillary  action,  we  are  on 
the  dividing  line  between  sound  ware  and  damaged  ware. 
When  capillarity  brings  the  water  to  the  surface  faster  than 
it  is  evaporated  from  the  surface,  the  ware  will  dry  safely  re- 


CLAYWORKING  PROBLEMS  167 

gardless  of  temperature,  assuming,  of  course  that  the  ware  is 
symmetrical  in  shape  and  dries  uniformly. 


Stiff  Mud  Brick  Break  in  Drying 

49.  Missouri— We  are  hat-ing  trouble  with  our  stiff-mud 
pressed  brick.  They  break  so  badly,  while  drying  on  the  yard, 
as  to  almost  destroy  the  profits.  We  burn  them  very  hard, 
but  still  they  are  very  brittle.  We  are  using  the  old-fash- 
ioned kilns.  The  clay  has  just  enough  sand  in  it  to  make  it 
mold  zvell.  We  would  be  glad  to  get  some  pointers  for  over- 
coming the  trouble. 

In  regard  to  the  troubles  of  "Missouri",  we  hesitate  to 
give  any  opinion  whatever  because  the  data  is  not  sufficient. 

Brick  break  from  a  number  of  causes  and  one  cannot  tell 
at  long  range  just  what  the  cause  may  be.  Clays  are  very 
uncertain  in  behavior  and  anyone  who  gives  an  opinion  of 
a  material,  or  an  explanation  of  a  trouble,  without  knowing 
the  material  and  investigating  the  trouble,  is  merely  guess- 
ing or  at  best  assuming  the  clay  to  be  of  a  certain  class  and 
the  trouble  to  have  a  certain  cause.  Based  upon  ihis  as- 
sumption one  gives  an  opinion,  but  it  may  not  at  all  fit  the 
specific  case. 

Brick  oftentimes  crack  and  break  in  the  burning  and  the 
fault  is  attributed  to  the  burning  process,  to  the  kilns  per- 
haps or  to  the  carelessness  of  the  burner,  when  it  may  be 
that  the  trouble  did  not  belong  to  the  kiln  at  all.  It  may 
have  been  the  quality  of  the  clay,  it  may  have  been  due  to 
machine  troubles  introducing  weaknesses  into  the  brick,  or 
the  trouble  may  have  originated  in  the  dryer  and  only  be- 
came apparent  after  the  product  was  burned,  yet.  on  the  other 
hand,  there  are  troubles  which  begin  and  end  in  the  kiln. 

The  trouble  in  the  dryer  may  be  due  to  the  type  of  the 
dryer,  to  the  drying  behavior  of  the  clay  or  to  the  machine. 
By  changes  in  the  clay  mixture  we  can  frequently  overcome 


168  CLAYWORKING  PROBLEMS 

difficulty  in  the  dryer  without  any  change  in  the  dryer,  and 
frequently  we  can  improve  the  machine  structure  of  the 
brick  and  overcome  the  dryer  difficulty,  but  on  the  other 
hand  it  sometimes  happens  that  the  dryer  itself  is  at  fault. 
Each  variety  of  clay  requires  very  different  treatment  in 
order  to  dry  it  safely  and  each  treatment  requires  special 
dryer  conditions. 

In  view  of  all  these  difficulties  it  is  absurd  for  anyone 
to  advise  another  without  some  personal  knowledge  of  the 
difficulty.  In  spite  of  this,  however,  it  seems  to  us  that 
"Missouri's"  clay  is  one  of  those  fine  grained  materials 
which  has  a  weak  structure  and  consequently  it  may  break 
very  easily  under  drying  strains.  Such  clays  when  burned 
very  hard  are  brittle,  largely  because  of  their  uniformity 
and  fineness  of  grain.  They  have  no  body,  no  skeleton 
structure;  in  fact,  they  are  like  a  piece  of  brittle  glass  and 
any  changes  in  temperature  in  the  burning  will  cause  them 
to  break,  and  after  they  are  burned  they  are  likewise 
easily  broken  because  of  their  brittleness. 

If  his  clay  does  not  contain  an  excess  of  sand  it  may 
be  that  the  clay  will  stand  more  dead  material  and  we 
would  suggest  the  use  of  coarsely  ground  kiln  clinkers, 
which  make  an  excellent  binder.  It  seems  to  us  that 
the  weakness  of  his  clay  can  be  overcome  by  the  addi- 
tion of  some  sort  of  binding  material,  and  crushed  bats 
or  crushed  kiln  clinkers  are  the  best  binders  we  know. 
The  addition  of  coarse  sand  might  accomplish  something, 
but  it  is  not  as  good  a  binder  as  the  other  materials  men- 
tioned. 

We  merely  suggest  this  as  a  possible  solution  to  his 
difficulty,  and  the  expense  of  making  a  test  along  this  line 
will  be  a  small  matter. 


More  Scum  Trouble 

240.     Kansas — I    make   a   stiff -mud    brick    and   find    that   it 


CLAYWORKING  PROBLEMS 


shows  scum  on  one  side  and  on  the  tivo  ends.  The  side  that 
fosses  over  the  rollers  of  the  off-cutting  table  does  not  scum 
to  speak  of.  The  die  is  lubricated  by  -water. 

Assuming  that  the  die  lubrication  is  distributed  evenly  to  all 
four  sides,  the  clay  column  is  exposed  to  the  same  condition 
at  top,  bottom  and  sides,  and  the  passing  over  the  rollers  of 
the  cutting  table  would  not  affect  it  sufficiently  to  prevent 
any  one  of  the  surfaces  becoming  scummed  in  the  dryer  or 
kiln,  if  the  tendency  to  scum  was  in  the  clay  or  the  green 
brick.  We  hazard  a  guess,  however,  that  the  manner  of 
setting  the  brick,  either  on  the  dryer  car  or  in  the  kiln,  is 
such  that  the  faces  and  ends  of  the  brick  are  exposed,  and 
the  backs  of  the  brick  set  close  together.  The  bottom  of  the 
clay  column,  which  passes  over  the  rollers  of  the  cut-off, 
having  taken  the  form  of  brick,  rests  upon  the  off-bearing 
belt,  which  may  mark  it.  This  would  make  that  side  (the 
lower)  the  "back."  The  idea  that  the  change  occurs  at  the 
cutting  table  can  be  eliminated  by  marking  some  of  the  brick 
"T"  for  top  of  co!umn  and  some  "B"  for  bottom  of  column, 
and  then  seeing  that  the  sides  so  marked  are  all  treated  as 
"backs"  and  so  set  on  the  dryer  cars  and  in  the  kilns.  Read 
Professor  Binn's  article  on  efflorescence  in  the  Nov.  18  issue 
of  this  magazine  and  do  some  experimenting  with  your  clay. 
Watch  the  water  very  carefully,  also — not  only  the  pugging 
water,  but  the  water  you  are  using  for  lubrication. 


Seems  to  Have  the  Old  Scum  Trouble 

489.  Ontario — We  are  making  a  wire-cut  brick,  using  a 
Freese  cutter  and  lubricating  the  bar  with  castor  oil.  The 
brick  are  being  dried  in  a  continuous  tunnel  dryer,  the  heat 
for  which  is  supplied  by  a  waste  heat  system,  supplemented 
by  an  auxiliary  wood  furnace.  We  are  troubled  with  a  white 
mark  on  the  surface  of  the  brick.  This  white  mark  is  discern- 
ible on  the  brick  as  they  come  from  the  dryer.  We  have 


CLAYWORKING  PROBLEMS 


thought  it  to  be  caused  by  the  oil  zve  arc  using,  or  possibly 
by  the  ashes  from  the  auxiliary  furnace  settling  on  the  oily 
surfaces.  Can  you  recommend  to  us  some  brand  of  oil  that 
will  cure  this  trouble,  of  suggest  some  other  remedy? 

We  do  not  believe  that  the  oil  has  anything  to  do  with 
the  matter,  and  are  under  the  impression  that  your  trouble 
is  as  old  as  brickmaking  itself — or  at  least  as  old  as  artificial 
drying  and  burning  with  coal.  It  looks  like  "scum,"  about 
which  every  man  who  has  written  about  brickmaking  has,  or 
will,  at  some  later  day,  write  one  or  more  articles.  Scum, 
or  efflorescence  is  caused  by  salts  in  the  clay.  These  are  de- 
veloped, sometimes,  in  the  dryer,  while  again  they  may  not 
show  until  the  brick  are  burned.  And  then  again,  many  in- 
stances are  known  where  the  "scum"  does  not  show  until 
the  brick  have  been  built  into  the  wall.  We  would  advise, 
first,  that  you  dry  at  least  one  car  of  brick  in  the  open  air, 
under  shed  cover,  and  where  it  is  not  exposed  to  any  sulphur 
fumes  from  burning  coal.  If,  when  they  are  bone  dry,  they 
show  no  white  mark,  you  will  have  located  a  part  of  your 
trouble — that  is,  that  the  dryer  brings  out  the  "scum."  Then 
go  after  the  scum  with  carbonate  of  barytes. 


Dry  Pan  Capacity. 

5.").  Texas — Kindly  ad?'ise  us  as  to  whether  one  nine-foot 
dry  pan  will  be  sufficient  for  grinding  material  of  the  soft 
fire-clay  variety  for  tzvo  four-mold  presses  to  manufacture 
forty  thousand  high  grade  manganese  face-brick  per  day. 
Would  also  appreciate  information  as  to  the  use  of  manganese 
—that  is  what  proportion  should  be  used  per  thousand  brick. 

No  one  can  predetermine  how  much  clay  one  pan  will  grind. 
It  is  customary  to  lay  out  a  plant  with  one  pan  for  each 
four-mold  press  but  frequently  clays  are  found  that  grind  and 
screen  so  rapidly  as  to  make  it  possible  for  one  pan  to  grind 
all  of  the  clay  for  two  presses.  If  the  clay  is  of  the  character 
which  insures  its  being  easily  ground,  you  are  safe  in  install- 


CLAYWORKING  PROBLEMS  171 

ing  a  single  pan  for  forty  thousand  brick  but,  since  there  is 
an  element  of  doubt,  it  is  well  for  you  to  provide  for  a  second 
pan,  even  going  as  far  as  to  build  the  foundations  for  it. 

The  chances  are,  however,  that  if  you  intend  making  a  high 
grade  product  which  will  require  finely  screened  clay,  two 
pans  will  be  necessary  and  both  will  be  run  to  their  maximum 
capacity. 

Regarding  the  use  of  manganese — it  is  well  to  provide,  in 
the  first  place,  for  a  measuring  device  and  so  secure  a  uni- 
form proportion  of  ground  clay  and  manganese.  Otherwise 
there  will  be  a  distinct  difference  in  the  color  of  the  product 
and  this  will  necessitate  a  great  deal  of  sorting  and  a  large 
number  of  small  hacks  that  do  not  "match  up"  to  the  stand- 
ard product  of  the  plant.  It  is  recommended  at  times  that 
this  manganese  be  fed  into  the  pan  but  this  is  not  so  practical 
as  arranging  for  a  proper  mixing  of  the  clay  and  manganese 
after  the  clay  has  been  reduced  to  the  proper  fineness  and 
been  passed  through  the  screen.  The  reasons  for  this  are 
obvious.  The  degree  of  fineness  to  which  the  manganese  is 
ground  before  it  is  mixed  into  the  clay  has  a  material  effect 
upon  the  depth  of  color  in  the  finished  product.  The  amount 
of  manganese  which  should  be  used  can  be  determined  only 
by  experiment  as  nearly  every  clay  needs  a  different  amount 
of  manganese  in  order  to  produce  a  given  result. 


Tile  Cracks  in  Drying 

687.  Iowa — This  plant  has,  ever  since  it  started,  been  both- 
ered with  the  tile  cracking  tchile  it  was  in  the  dry  sheds.  We 
use  surface  clay,  mixing  the  four  top  spades.  The  two  top 
spades  are  a  very  dark  clay  and  the  two  lower  ones  are  yel- 
low or  bluish  clay.  They  are  mixed  after  removing  about 

eight  inches  of  over-burden.     We  use  a  machine 

with  a  bridge  just  back  of  the  dies,  with  a  stem,  on  it  to  hold 
the  core  or  center  piece.  There  is  only  about  eight  inches 
between  the  die  and  the  bridge  for  the  clay  to  unite  and  I 


172  CLAYWORKING  PROBLEMS 

have  thought  that  a  great  deal  of  the  cause  of  the  cracking 
was  due  to  this  bridge  cutting  the  clay  up  b'efore  it  went 
through  the  die.  I  cannot  bclie-rc  that  ours  is  a  bad  clay  but 
do  believe  that  the  main  fault  is  in  the  machine. 

Before  answering  this  question  it  was  necessary  to  write 
our  correspondent  asking  for  more  information  in  connec- 
tion with  his  process,  particularly  in  connection  with  clay 
preparation  and  the  answer  follows : 

My  clay  is  hauled  in  the  clay  shed  with  cars  and  I  keep  one 
man  in  the  shed  to  level  it  off  as  it  is  dumped,  so  that  it  will 
get  mixed  thoroughly.  It  is  very  wet  now  and  I  grind  the 
broken  tile  in  the  sheds,  using  a  dry  pan  and  then  mix  the 
ground  burned  clay  with  the  ra^u  clay  and  this  makes  it  stiff 
enough  to  insure  the  ware's  coining  from  the  machine  suffi- 
ciently stiff  to  permit  of  its  being  handled.  The  clay  is  shov- 
eled on  to  a  belt  or  clay  conveyor  and  is  dumped  from  that  in- 
to the  crusher  rollers  which  set  above  the  machine.  This  ma- 
chine is  a  pug  mill  and  auger  machine  combined,  consisting  of 
an  eight-foot  pug  mill  with  about  three  feet  of  augers.  I  de- 
pend upon  the  pug  mill  to  do  tlic  tempering.  When  my  clay 
gets  dry  enough  I  use  water  in  the  pug  mill  and  zvould  say 
that  this  water  comes  from  the  supply  tank  to  the  boiler.  It  is 
neither  hot  nor  cold  but  just  a  little  warm.  When  the  clay  is 
wet,  as  it  is  at  present,  I  do  not  use  any  tempering  water  at  all. 
You  will  understand  that  I  use  the  dry  pan  only  to  grind 
broken  tile,  but  do  not  use  it  in  connection  with  the  raw  clay. 
The  bridge  plates  in  the  machine  are  rough  (corrugated).  The 
tile  crack  lengthwise  when  run  soft  and  when  run  very  still, 
they  have  a  few  cracks  which  run  around  them.  Some  will 
check  two  or  three  inches  into  the  end  and  others  will  crack 
clean  through.  I  have  some  five-inch  tile  in  the  shed  now  that 
have  cracked  in  three  places  and  have  come  apart  into  three 
pieces.  These  cracks  are  exactly  where  the  wings  are  on  the 
bridge.  It  depends  on  the  iveather  when  they  start  cracking. 
If  the  weather  is  warm  and  dry,  they  will  start  cracking  about 
the  third  day  after  they  are  put  in  the  shed  but  if  it  is  wet 


CLAYWORKING  PROBLEMS  173 

and  cool,  they  will  not  crack  until  about  the  fifth  day.  As 
soon  as  I  notice  them  starting  to  check,  I  put  the  men  in  the 
shed  and  turn  over  the  tile  end  for  end;  this  seems  to  help  and 
stops  any  more  from  cracking,  but  this  process  is  expensive, 
and  if  the  tile  are  allowed  to  go  too  long  without  turning, 
there  is  an  awful  waste.  I  cannot  say  that  there  is  any  "safe" 
period  when  the  tile  do  not  crack,  only  as  I  have  stated  above. 
After  the  tile  are  in  the  shed  (which  is  a  natural  air  dryer 
with  doors  on  the  side  to  raise  and  lower)  I  leave  these  doors 
closed  until  the  tile  are  well  set  and  have  started  to  dry; 
then  I  open  the  doors  on  the  opposite  side  from  the  wind,  but 
not  on  both  sides,  until  the  tile  are  about  two-thirds  dry.  At 
that  time  I  figure  that  if  the  wind  is  not  too  strong,  it  will 
not  harm  them  to  open  the  doors  on  both  sides.  It  takes  me 
from  two  to  four  weeks  before  the  tile  are  ready  for  the  kiln. 
Answering  your  questions  as  to  the  formation  of  the  die,  etc., 
n'ould  repeat  what  I  have  already  said  regarding  the  bridge 
which  is  that  it  sets  about  eight  inches  back  of  the  die  and 
that  the  core  is  fastened  to  it  (the  bridge).  The  augers  are 
about  three  inches  back  of  the  bridge.  The  five-inch  and  six- 
inch  are  the  ivorst  sizes  for  cracking,  although  the  other  sises 
crack  a  great  deal  more  than  they  ought.  The  walls  of 
my  five-inch  are  three-quarters  of  an  inch  thick  and  the  walls 
of  the  six-inch  are  thirtccn-sixtcenths  of  an  inch  thick.  The 
tile  arc  cut  thirteen  inches  long  and  the  shrinkage  in  drying 
is  three-eights  of  an  inch  in  diameter.  The  shrinkage  in 
burning  is  one-eighth  of  an  inch.  This  burning  shrinkage 
is  increased  in  the  case  of  the  tile  that  are  set  right  around 
the  fire  boxes  and  where,  as  a  rule,  the  tile  are  burned  black. 
Here  the  five-inch  will  shrink  one-quarter  of  an  inch  and  the 
six-inch  will  shrink  just  a  little  more  than  this.  The  augers 
I  am  using  at  the  present  time  were  new  in  April  of  this  year 
and  I  estimate  that  they  have  not  made  more  than  one  hun- 
dred thousand  tile.  My  five-inch  and  six-inch  dies  were  new 
in  the  spring  of  nineteen-fourteen.  The  five-inch  die  has 
made  about  two  hundred  and  twenty-five  thousand  tile  and 


174  CLAYWORKING  PROBLEMS 

the  six-inch  die  has  made  about  one  hundred  thousand.  Re- 
garding the  other  dies,  I  fear  that  I  could  not  say  how  old 
they  are  or  how  many  tile  they  have  made. 

A  short  time  ago,  Professor  Stull  (then  of  the  University 
of  Illinois)  wrote  in  connection  with  an  answer  that  he  made 
through  this  department  that  it  was  often-times  as  difficult 
and  practically  impossible  to  give  a  remedy  for  a  manufac- 
turing defect  as  it  was  impractical,  and  generally  impossible, 
for  a  physician  to  prescribe  for  an  ailment  that  was  described 
to  him  by  mail.  The  patient  has  a  way  of  telling  all  of  the 
symptoms  excepting  the  one  which  will  lead  to  the  correct 
diagnosis. 

In  a  case  of  that  kind  the  doctor  can  do  but  little  more 
than  hazard  a  guess  and  since  our  correspondent  has  gone 
to  the  trouble  of  describing  his  problem  so  minutely,  "Brick 
and  Clay  Record"  will  hazard  a  guess  and  it  is  that  the 
trouble  lies  largely  in  the  thickness  of  the  walls  of  the  tile. 
We  would  suggest  that  the  five-inch  tile  be  reduced  to  one- 
half  inch  thickness  (burned)  and  the  six-inch  tile  to  be 
between  nine-sixteenths  and  five-eighths  (burned).  This 
thickness  gives  sufficient  strength  and  allays  in  great  measure 
any  tendency  toward  unequal  drying.  It  is,  as  a  rule,  un- 
equal drying  that  causes  the  split  cracks  along  the  line  of 
the  three  core  supports  or  the  spider  bridge. 

It  would  be  well  to  wrap  a  few  wires  around  the  bridge 
plates  in  order  that  the  clay  passing  into  the  die  may  be 
torn  up  and  the  chances  for  rebonding  increased. 

There  is,  from  the  description  that  has  been  given,  a  great 
likelihood  that  the  clays  are  not  thoroughly  mixed  as  they 
come  from  the  pit.  One  man  in  a  dry  shed  may  be  capable 
of  doing  this  work  but  there  is  a  good  chance  that  he  is 
not  doing  it.  If  it  were  possible  to  install  a  mechanical  clay 
mixer,  this  machine  would  be  very  liable  to  pay  for  itself 
in  a  very  short  time,  if  not  in  labor  saving,  then  in  better 
ware. 

There    seems   to   be   a   hit-and-miss    method    in    connection 


CLAYWORKING    PROBLEMS 


with  the  addition  of  dry  ground  clay  to  the  wet  clay  and 
there  is  a  great  question  as  to  whether  the  same  results  will 
be  obtained  in  drying  and  burning  ware  that  is  made  from 
three  different  clay  propositions.  This  correspondent  has, 
first;  semi-wet  clay  that  is  used  without  the  addition  of  grog 
and  without  tempering  water ;  second ;  wet  clay  that  is  mixed 
with  grog ;  third ;  dry  raw  clay  that  has  to  be  mixed  with 
tempering  water.  Any  number  of  experiments  could  be 
made  and  improvements  added  to  a  drying  process  but  when 
they  were  all  finished,  they  would  not  give  any  definite  re- 
sults for  the  reason  that  it  would  be  hard  to  calculate  the 
basis — that  is,  the  exact  character  of  the  clay  upon  which  the 
experiments  were  made.  This  takes  us  back  to  the  question 
of,  in  the  first  place,  a  proper  clay  mixing  machine  and  it 
looks  as  though  this  plant  could  use  to  advantage  some  in- 
expensive clay  storage  system  which  would  provide  for  the 
clay's  being  brought  in  and  stored  in  an  open  shed  where  it 
can  be  air  dried.  This  shed  could  be  so  arranged  as  to  be 
in  itself  a  clay  mixing  apparatus.  There  is  no  doubt  but  that 
it  would  improve  the  c'ay  to  be  weather  slaked  and  weather 
dried  before  going  to  the  crushing  rolls. 

In  this  way  a  mixture  will  be  assured  that  is  reasonably 
uniform,  not  only  as  to  the  proportions  of  the  clays  that 
compose  it,  but  the  dryness  of  these  c!ays.  This  condition 
will  insure  the  amount  of  tempering  water — that  is,  no  more 
tempering  water  will  be  required  at  one  time  than  at  an- 
other and,  as  a  consequence,  some  dependency  can  be  placed 
upon  the  action  of  this  tempering  water — a  matter  that  is 
very  much  in  doubt  at  the  present  time. 

There  is  reason  to  believe  that  the  nose  of  the  auger  is 
too  close  to  the  bridge  and  it  would  be  well  to  place  a  wooden 
washer  about  two  inches  think  between  the  bridge  and  the 
die  support  (or  head-piece)  and  the  barrel  of  the  machine. 
This  will  shove  the  die  about  two  inches  farther  from  the 
auger  then  it  at  present  is  and  the  pressure  will  not  be  so 
intense  on  the  clay  passing  the  bridge.  This  will  have  a 


CLAYWORKING    PROBLEMS 


tendency  to  prevent  the  "shining  up"  of  the  clay  and  so  help 
it  to  knit  together  as  it  passes  through  the  die. 

There  is  also  a  possibility  that  the  forms  on  your  auto- 
matic cutter  may  be  too  small  and  in  this  way,  the  tile  may 
be  squeezed  and  bridge  cracks  open  up.  The  same  may 
happen  in  handling. 

Another  point  is  that  your  tile  should  be  just  hard  enough 
to  handle  safely;  too  stiff  is  just  as  injurious  as  too  soft. 

Best  of  all — since  this  correspondent  says  that  the  trouble 
in  question  has  existed  for  years,  (and  it  is  to  be  presumed 
that  during  these  years  the  yard  has  had  several  superin- 
tendents) much  could  have  been  saved  by  the  employment 
of  an  expert  "trouble  doctor"  several  years  ago.  Too 
many  owners  of  clay  plants  and  too  many  superintend- 
ents are  disinclined  to  admit  that  they  have  met  with  a 
problem  that  is  entirely  beyond  them.  They  have  a  way 
of  experimenting  and  of  trying  to  do  away  with  the  trouble 
without  expert  advice  and  in  this,  the  man  who  prefers 
to  dose  himself  with  patent  medicines,  rather  than  submit 
to  a  thorough  medical  examination  by  an  approved  prac- 
titioner, they  meet  with  but  little  success  and  an  organic 
disease  grows  worse  with  the  years.  In  this  case  the  "or- 
ganic disease"  seems  to  be  eating  its  way  into  the  bank  ac- 
count and  there  seems  reason  to  say  that  the  hiring  of  an 
expert,  even  though  it  necessitate  the  expenditure  of  a  sum 
that  would  be  several  times  as  great  as  that  paid  to  the  super- 
intendent, would  stop  a  leak  which  is  seriously  threatening 
the  well  being  of  this  plant. 


The  Question  of  a  Second  Machine 

695.  Iowa — We  have  a  steam  dryer  and  our  clay,  while 
very  slow  to  dry,  works  all  right  if  the  dryer  is  not  rushed. 
W e  are  considering  the  advisability  of  installing  a  second  ma- 
chine so  that  we  could  run  part  time  on  drain  tile  or  hollow 
block  and  part  time  on  brick.  At  present  if  I  change  the  ma- 


CLAYWORKING   PROBLEMS 177 

chine  die  from  hollow  ware  to  make  brick,  I  get  too  much 
brick  in  the  dryer.  If  I  could  keep  a  quantity  of  drain  tile, 
hollow  block  and  brick  in  the  dryer  I  could  take  them  out  and 
burn  them  as  I  wanted  to — the  tile  soft  and  the  brick  and 
blocks  harder.  I  hare  a  forty  H.P.  motor  which  gives  just 
enough  power  to  run  the  one  machine.  Could  I  run  it  on  a 
main  shaft  and  then  over  to  the  two  machines,  running  only 
one  at  a  time?  In  other  words,  does  running  to  a  line  shaft 
tvcaken  the  power? 

If  your  plan  is  to  obviate  any  loss  of  time  in  changing  the 
dies  then  it  is  an  excellent  scheme  to  have  two  machines. 
Otherwise  the  only  advantage  that  you  would  get  is  that  you 
would  have  some  insurance  against  shut-downs,  due  to  either 
of  the  machines  breaking  down.  Another  advantage  is,  possibly 
that  you  could  adjust  the  machine  that  made  your  hollow 
ware  so  as  to  work  better  on  that  particular  kind  of  material 
and  you  could  certainly  get  a  more  exact  adjustment  on  the 
machine  which  worked  on  brick  alone.  In  other  words,  you 
could  make  both  of  the  machines  "specialize"  on  the  product 
that  they  were  producing  and  in  this  way  get  a  great  economy 
out  of  both. 

The  question  of  setting  one  ware  on  the  other  in  the  dryer 
in  such  quantity  as  to  allow  you  to  draw  one  kind  of  ware 
or  the  other  would  not,  according  to  our  way  of  thinking, 
be  settled  by  the  installation  of  a  second  machine.  It  seems 
to  be  more  a  case  of  calculating  just  what  ware  you  want 
to  set  and  how  much  of  it,  and  then  making  just  that  amount 
of  ware.  Certainly  this  situation  would  not  be  improved  by 
having  a  second  or  even  a  third  machine — that  is,  unless  you 
are  using  a  differently  tempered  clay,  or  a  different  clay  al- 
together for  the  various  kinds  of  ware  that  you  are  making. 
In  that  event,  different  pug  mills  would  be  an  advantage  as 
well  as  different  machines  and  dies. 

In  belting  your  motor  to  a  main  line  shaft  and  then  string- 
ing two  belts— one  to  each  machine— you  have  an  additional 
load  to  carry,  due  to  the  friction  of  your  shaft  on  its  bear- 


178  CLAYWORKING    PROBLEMS 

ings  and  the  power  required  to  turn  over  the  additional  trans- 
mission machinery.  The  power  dropped  should  not  exceed 
five  per  cent,  or  approximately  two  and  a  half  H.P.  There- 
fore, unless  you  can  safely  overload  your  40  H.P.  motor, 
your  available  transmitted  power  would  be  about  37^2  H.P. 

Difficulty  in  Grinding  Wet  Shale 

699.  Minnesota — We  arc  having  difficulty  in  getting  wet 
shale  through  our  dry  pan.  Can  you  suggest  the  cheapest 
and  best  remedy? 

Temporary  relief  may  be  obtained  by  mixing  the  setter's 
waste  (that  is,  the  unburned  ware  which  comes  to  the  kilns, 
but  which  is  not  sufficiently  perfect  to  set)  with  the  wet 
shale  that  is  fed  to  the  dry-pans ;  this,  however,  is  only  tem- 
porary, since  all  of  the  available  dried  clay  will  be  used  up 
in  a  very  short  time.  We  are  assuming  that  you  are  already 
using  all  of  the  broken  burned  ware  that  your  clay  will 
stand. 

On  the  other  hand,  there  are  clay  driers  advertised  in 
"Brick  and  Clay  Record"  that  would  take  care  of  your 
problem  and  do  it  in  a  very  satisfactory  manner.  This, 
however,  is  an  installation  that  attains  its  maximum  efficiency 
when  the  clay  is  wet  all  through  the  year,  which  we  assume 
is  not  your  case. 

Your  remedy  seems  to  lie  in  installing  a  clay  storage  sys- 
tem with  conveyors  that  will  handle  the  clay  after  it  has 
been  weather-dried.  That  will  insure  a  better  clay  mixture 
and — at  least  in  the  majority  of  cases — a  better  and  more 
uniform  product. 


Discoloration  in  Painted  Hollow  Tile  Walls 

703.  Pennsylvania — In  several  cases,  where  plaster  has 
been  applied  to  the  inner  surface  of  our  hollow  clay  tile  or 
clay  tile  furring,  and  then  painted,  it  has  been  noticed  that 
the  paint  blisters,  bubbles  or  discolors.  We  hare  a  case  at 


CLAYWORKING   PROBLEMS  179 

present,  in  which  our  tile  was  used  for  the  zvalls  of  a  church. 
The  plaster  was  applied  directly  to  the  tile  walls,  and  an  oil 
paint  immediately  put  on  the  plaster.  Large  blisters  or  bub- 
bles— some  of  them  as  large  as  a  man's  hand — are  now  form- 
ing on  the  walls,  and  under  these  blisters  or  bubbles,  a 
creamy,  granular  substance  appears  that  has  a  decidedly  salty 
taste.  There  is  a  great  deal  of  talk  about  the  occurrence, 
and  some  interests  are  trying  to  blame  the  tile.  We  feel  that 
the  tile  is  in  no  way  to  blame.  We  have  had  numerous  build- 
ings erected  where  a  lime  mortar  is  used  and  in  these  we 
have  had  no  trouble  with  any  deposit  or  efflorescence.  Our 
tile  is  frequently  left  on  the  hack  heaps  for  nine  months  or 
more  and  in  no  case  have  we  found  any  discoloration  upon 
it.  We  do  find,  however,  that  when  the  tile  is  laid  up  zvith 
cement  mortar,  an  efflorescence  appears  on  the  tile  around  the 
joints.  We  have  had  our  tile  tested,  and  the  absorption  is 
under  two  per  cent.  In  the  case  alluded  to  earlier  in  this  let- 
ter, cement  mortar  zi'as  used,  and  we  feel  that  the  paint  was 
applied  to  the  plaster  before  it  (the  plaster)  was  dry,  and 
perhaps  before  the  cement  joint  had  been  given  an  oppor- 
tunity to  thoroughly  dry  out.  We  feel  that,  in  this  case,  the 
plaster  has  absorbed  or  combined  zvith  the  salts  in  the  cement 
mortar  joints  and  has  taken  the  substance  that  causes  the 
blisters  in  the  paint,  from  the  cement.  We  would  like  to  hear 
from  you  as  to  whether  you  know  anything  about  similar 
occurrences  and  whether  or  not  there  is  a  way  of  preventing 
them.  We  have  suggested  the  use  of  a  waterproofing  com- 
pound in  the  mortar,  but  several  masons  and  plasterers,  zvith 
whom  zvc  have  consulted,  tell  us  that  there  is  no  satisfactory 
zt'aterproofing  compound  made  that  can  be  used  in  this  way. 
They  say  that  the  only  satisfactory  treatment  is  to  use  a  zva- 
terproofing  paint,  applied  directly  to  the  entire  inner  surface 
of  the  tile  wall,  and  as  we  all  knozv,  this  is  too  expensive  a 
process  to  be  considered  as  a  commercial  proposition,  at  least 
in  a  large  number  of  building  enterprises. 

We  are  of  the  opinion  that  the  trouble  which  has  arisen 
in   the  case  mentioned  is  due  entirely  to  the  paint's  having 


180  CLAYWORK1NG    PROBLEMS 


been  applied  to  the  plaster  before  the  latter  had  been  thor- 
oughly dried,  and  that  the  blisters  in  the  paint  were  caused 
by  the  evaporating  moisture  in  the  plaster  (and  perhaps,  the 
joint)  which  was  seeking  an  outlet.  Plaster  is,  and  has  been 
applied  directly  to  the  inner  surface  of  tile  walls,  all  over 
the  country,  and  so  far  has  given  very  satisfactory  results, 
the  case  cited  by  our  correspondent  being  one  of  very  few 
that  have  come  to  our  notice.  This  opinion  is  strengthened 
by  the  fact  that  the  correspondent's  tile  has  a  very  low 
absorption — much  lower  than  the  average.  This,  and  the  fact 
that  he  has  never  had  any  efflorescence  appear  on  the  tile 
that  was  hacked  in  his  yard — even  after  an  exposure  of  more 
than  nine  months — is  pretty  good  evidence  that  the  treatment, 
and  not  the  tile,  is  at  fault.  It  looks  very  much  as  though 
the  blistering  was  due  to  some  constructional  fault  and  this 
may  be  the  use  of  cement  with  tile  of  so  low  an  absorption. 
The  fact  that  the  tile  takes  comparatively  none  of  the  mois- 
ture from  the  cement  leaves  only  the  inner  and  outer  sur- 
faces of  the  joint  as  points  where  the  excess  moisture  can 
escape.  It  may  be  that  the  outer  surface  of  the  joint  dried 
out  much  more  quickly  than  the  inner  surface,  particularly 
as  this  inner  surface  was  again  wetted  when  the  plaster  was 
applied  to  it.  Capillary  attraction  may  have  been  set  up  that 
brought  out  all  of  the  salt  that  was  in  the  cement,  or  in  the 
water  with  which  the  cement  was  mixed  (see  "How  to  Pre- 
vent Efflorescence  in  Finished  Brickwork"  in  the  Sept.  7  issue 
of  "Brick  and  Clay  Record")  and  that  the  plaster  would  have 
been  scummed,  even  if  not  painted.  This  thing  has  happened 
in  buildings  where  impervious  paving  brick  were  used  and 
where  plaster  was  applied  without  furring.  In  that  case  it 
was  clearly  the  fault  of  applying  the  plaster  before  the  cement 
joint  had  been  given  an  opportunity  of  drying  out,  and  was 
caused  by  the  church  committee's  insisting  upon  the  contrac- 
tor's turning  over  a  finished  building  within  a  certain  speci- 
fied time.  In  the  case  cited  by  our  correspondent  the  mois- 
ture in  the  plaster  was  held  back  by  the  comparatively  im- 
pervious paint  film  that  was  put  on  by  the  decorator,  and 


CLAYWORKING   PROBLEMS  181 

the  conditions  made  so  much  the  worse.  With  regard  to 
the  appearance  of  efflorescence  around  the  cement  joints,  it 
would  appear  that  this  is  a  problem  that  can  be  solved  by  the 
use  of  barium.  We  again  refer  our  readers  to  the  article 
by  Arthur  E.  Williams  in  the  Sept.  7  issue  of  this  magazine. 


Brick  and  Clay  Record's 

nrHESE  BOOKS  have  been  selected  as  having  especial  in- 
-*•  tercst  and  value  to  the  clayworker.  They  are  confidently 
offered  as  the  best  printed  information  on  'the  subjects  cov- 
ered that  has  appeared  in  book  form  and  in  the  English  lan- 
guage. Any  book  in  the  following  list  unll  be  sent  on  receipt 
of  price.  None  Zfill  be  sent  on  approval. 

Brick  Drying  (English  Edition)  .$1.00 

Brick  Houses  and  How  to  Build 

Them  (Radford) i.oo 

Bungalows,  Camps  and  Mountain 

Houses 2,00 

Ceramic  Calculations 1.20 

Clay  Glazes  and  Enamels  (Grif- 
fin)     5.00 

Clay  workers'  Handbook  (Searle)  2.00 

Engineering  for  Land  Drainage 

(Elliott)    2.00 

Estimating  and  Contracting  (Rad- 
ford)       2.00 

Garage  and  Motor  Boat  Houses.  .  i.oo 

The  Glazer's  Book  (Raes) i.oo 

The  Hollow  Tile  House  (Squiers)  2.50 

How  to  Analyze  Clay  ( Ashby) .  .  .  i.oo 

182 


Book    Department 

The  Manufacture  of  Glazed 

Bricks  (English  Edition)...  2,50 

The  Manufacture  of  Roofing  Tile 

(Worcester)    75 

The  Manufacture  of  Roofing  Tile 

(English  Edition) i.oo 

"Masonry"  (Howe) 1.50 

"Modern  Brickmaking"  (Searle) .  5.00 

One  Hundred  Bungalows  (BBA)     .50 

Pottery  (Cox) 1.25 

Practical    Brick   and   Tile    Book 

(Dobson- Hammond)    2.40 

Producer  Gas  and  Gas  Producers 

(Wyer)    4.00 

Refractories  and  Furnaces   (Ha- 

vard)    4.00 

Scumming  and  Efflorescence 

(Lovejoy)   50 

Seger's  Collected  Works  (Con- 
densed)    3-50 

Sewage  Disposal  Works:  Their 
Design  and  Construction 
(Easdale)  4-<>o 

183 


Brick  and  Clay  Record 

A    Semi-Monthly  Magazine  Special- 
izing   in  Clayworking  and  Ceramics 


Published  the  First 
and  Third  Tuesdays  in 
each  month  at  Chicago 


Subscription  Price  (One  Year)    $2.00 

($3.00  in  Canada  and   Foreign  Countries) 

Sample   Copy   Free    on    Request 
Brick    and    Clay    Record 

445  Plymouth  Court Chicago,  U.  S.  A. 


University  of  California 

SOUTHERN  REGIONAL  LIBRARY  FACILITY 

405  Hilgard  Avenue,  Los  Angeles,  CA  90024-1388 

Return  this  material  to  the  library 

from  which  it  was  borrowed. 


MAY  1  7  1993 
EMS  LIBRARY 


000768722     1 


TP 

827 

B76o 


Ubriry 

AUXILIARY 

SEP     73 


UniversJ 

South 

Libr 


STACK 


